Src homology 3 domain of Src-Like Adaptor Protein; SLAP (or SLA1) modulates TCR surface expression levels as well as surface and total BCR levels. As an adaptor to c-Cbl, SLAP increases the ubiquitination, intracellular retention, and targeted degradation of the BCR complex components. SLAP has been shown to interact with the EphA receptor, EpoR, Lck, PDGFR, Syk, CD79a, c-Cbl, LAT, CD247, and Zap70, among others. SLAPs are adaptor proteins with limited similarity to Src family tyrosine kinases. They contain an N-terminal SH3 domain followed by an SH2 domain, and a unique C-terminal sequence. The SH3 domain of SLAP forms a complex with v-Abl. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 194328725  43 FLAVLSDYPSPDISPPIFRRGEKLRVISDEGGWWKAISLSTGRESYIPGICVARV 97
Cdd:cd12010    1 FLAVLADYPSPDISEPIFHMGEKLRVLSDEGGWWKVRSLQTGRENYIPGKCVAKV 55

Src homology 3 domain of Src-Like Adaptor Protein; SLAP (or SLA1) modulates TCR surface expression levels as well as surface and total BCR levels. As an adaptor to c-Cbl, SLAP increases the ubiquitination, intracellular retention, and targeted degradation of the BCR complex components. SLAP has been shown to interact with the EphA receptor, EpoR, Lck, PDGFR, Syk, CD79a, c-Cbl, LAT, CD247, and Zap70, among others. SLAPs are adaptor proteins with limited similarity to Src family tyrosine kinases. They contain an N-terminal SH3 domain followed by an SH2 domain, and a unique C-terminal sequence. The SH3 domain of SLAP forms a complex with v-Abl. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 194328725  43 FLAVLSDYPSPDISPPIFRRGEKLRVISDEGGWWKAISLSTGRESYIPGICVARV 97
Cdd:cd12010    1 FLAVLADYPSPDISEPIFHMGEKLRVLSDEGGWWKVRSLQTGRENYIPGKCVAKV 55

SH2 domain;

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 194328725  101 WLFEGLGRDKAEELLqLPDTKVGSFMIRESETKKGFYSLSVRHR-QVKHYRIFRLPNNWYYISPRLTFQCLEDLVNHY 177
Cdd:pfam00017   1 WYHGKISRQEAERLL-LNGKPDGTFLVRESESTPGGYTLSVRDDgKVKHYKIQSTDNGGYYISGGVKFSSLAELVEHY 77

SH3 domain; SH3 (Src homology 3) domains are often indicative of a protein involved in signal transduction related to cytoskeletal organization. First described in the Src cytoplasmic tyrosine kinase. The structure is a partly opened beta barrel.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|
gi 194328725   42 DFLAVLSDypspDISppiFRRGEKLRVISD-EGGWWKAISLsTGRESYIP 90
Cdd:pfam00018   5 DYTAQEPD----ELS---FKKGDIIIVLEKsEDGWWKGRNK-GGKEGLIP 46

Src homology 2 (SH2) domain found in the Src family of non-receptor tyrosine kinases; The Src family kinases are nonreceptor tyrosine kinases that have been implicated in pathways regulating proliferation, angiogenesis, invasion and metastasis, and bone metabolism. It is thought that transforming ability of Src is linked to its ability to activate key signaling molecules in these pathways, rather than through direct activity. As such blocking Src activation has been a target for drug companies. Src family members can be divided into 3 groups based on their expression pattern: 1) Src, Fyn, and Yes; 2) Blk, Fgr, Hck, Lck, and Lyn; and 3) Frk-related kinases Frk/Rak and Iyk/Bsk Of these, cellular c-Src is the best studied and most frequently implicated in oncogenesis. The c-Src contains five distinct regions: a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. Src exists in both active and inactive conformations. Negative regulation occurs through phosphorylation of Tyr, resulting in an intramolecular association between phosphorylated Tyr and the SH2 domain of SRC, which locks the protein in a closed conformation. Further stabilization of the inactive state occurs through interactions between the SH3 domain and a proline-rich stretch of residues within the kinase domain. Conversely, dephosphorylation of Tyr allows SRC to assume an open conformation. Full activity requires additional autophosphorylation of a Tyr residue within the catalytic domain. Loss of the negative-regulatory C-terminal segment has been shown to result in increased activity and transforming potential. Phosphorylation of the C-terminal Tyr residue by C-terminal Src kinase (Csk) and Csk homology kinase results in increased intramolecular interactions and consequent Src inactivation. Specific phosphatases, protein tyrosine phosphatase a (PTPa) and the SH-containing phosphatases SHP1/SHP2, have also been shown to take a part in Src activation. Src is also activated by direct binding of focal adhesion kinase (Fak) and Crk-associated substrate (Cas) to the SH2 domain. SRC activity can also be regulated by numerous receptor tyrosine kinases (RTKs), such as Her2, epidermal growth factor receptor (EGFR), fibroblast growth factor receptor, platelet-derived growth factor receptor (PDGFR), and vascular endothelial growth factor receptor (VEGFR). In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVR------HRQVKHYRIFRLPNNWYYISPRLTFQCLEDLV 174
Cdd:cd09933    5 WFFGKIKRKDAEKLLLAPGNPRGTFLIRESETTPGAYSLSVRdgddarGDTVKHYRIRKLDNGGYYITTRATFPTLQELV 84

                         90
                 ....*....|....*..
gi 194328725 175 NHYSEVADGLCCVLTTP 191
Cdd:cd09933   85 QHYSKDADGLCCRLTVP 101

Src homology 3 domain of Src-Like Adaptor Protein; SLAP (or SLA1) modulates TCR surface expression levels as well as surface and total BCR levels. As an adaptor to c-Cbl, SLAP increases the ubiquitination, intracellular retention, and targeted degradation of the BCR complex components. SLAP has been shown to interact with the EphA receptor, EpoR, Lck, PDGFR, Syk, CD79a, c-Cbl, LAT, CD247, and Zap70, among others. SLAPs are adaptor proteins with limited similarity to Src family tyrosine kinases. They contain an N-terminal SH3 domain followed by an SH2 domain, and a unique C-terminal sequence. The SH3 domain of SLAP forms a complex with v-Abl. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 194328725  43 FLAVLSDYPSPDISPPIFRRGEKLRVISDEGGWWKAISLSTGRESYIPGICVARV 97
Cdd:cd12010    1 FLAVLADYPSPDISEPIFHMGEKLRVLSDEGGWWKVRSLQTGRENYIPGKCVAKV 55

Src homology 2 (SH2) domain found in Lyn; Lyn is a member of the Src non-receptor type tyrosine kinase family of proteins and is expressed in the hematopoietic cells, in neural tissues, liver, and adipose tissue. There are two alternatively spliced forms of Lyn. Lyn plays an inhibitory role in myeloid lineage proliferation. Following engagement of the B cell receptors, Lyn undergoes rapid phosphorylation and activation, triggering a cascade of signaling events mediated by Lyn phosphorylation of tyrosine residues within the immunoreceptor tyrosine-based activation motifs (ITAM) of the receptor proteins, and subsequent recruitment and activation of other kinases including Syk, phospholipase C2 (PLC2) and phosphatidyl inositol-3 kinase. These kinases play critical roles in proliferation, Ca2+ mobilization and cell differentiation. Lyn plays an essential role in the transmission of inhibitory signals through phosphorylation of tyrosine residues within the immunoreceptor tyrosine-based inhibitory motifs (ITIM) in regulatory proteins such as CD22, PIR-B and FC RIIb1. Their ITIM phosphorylation subsequently leads to recruitment and activation of phosphatases such as SHIP-1 and SHP-1 which further down modulate signaling pathways, attenuate cell activation and can mediate tolerance. Lyn also plays a role in the insulin signaling pathway. Activated Lyn phosphorylates insulin receptor substrate 1 (IRS1) leading to an increase in translocation of Glut-4 to the cell membrane and increased glucose utilization. It is the primary Src family member involved in signaling downstream of the B cell receptor. Lyn plays an unusual, 2-fold role in B cell receptor signaling; it is essential for initiation of signaling but is also later involved in negative regulation of the signal. Lyn has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRHRQ------VKHYRIFRLPNNWYYISPRLTFQCLEDLV 174
Cdd:cd10364    5 WFFKDITRKDAERQLLAPGNSAGAFLIRESETLKGSYSLSVRDYDpqhgdvIKHYKIRSLDNGGYYISPRITFPCISDMI 84

                         90
                 ....*....|....*..
gi 194328725 175 NHYSEVADGLCCVLTTP 191
Cdd:cd10364   85 KHYQKQSDGLCRRLEKA 101

Src homology 2 (SH2) domain found in Gardner-Rasheed feline sarcoma viral (v-fgr) oncogene homolog, Fgr; Fgr is a member of the Src non-receptor type tyrosine kinase family of proteins. The protein contains N-terminal sites for myristoylation and palmitoylation, a PTK domain, and SH2 and SH3 domains which are involved in mediating protein-protein interactions with phosphotyrosine-containing and proline-rich motifs, respectively. Fgr is expressed in B-cells and myeloid cells, localizes to plasma membrane ruffles, and functions as a negative regulator of cell migration and adhesion triggered by the beta-2 integrin signal transduction pathway. Multiple alternatively spliced variants, encoding the same protein, have been identified Fgr has been shown to interact with Wiskott-Aldrich syndrome protein. Fgr has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRH------RQVKHYRIFRLPNNWYYISPRLTFQCLEDLV 174
Cdd:cd10367    5 WYFGKIGRKDAERQLLSPGNPRGAFLIRESETTKGAYSLSIRDwdqnrgDHVKHYKIRKLDTGGYYITTRAQFDTVQELV 84

                         90
                 ....*....|....*..
gi 194328725 175 NHYSEVADGLCCVLTTP 191
Cdd:cd10367   85 QHYMEVNDGLCYLLTAP 101

Src homology 2 (SH2) domain found in Fyn; Fyn is a member of the Src non-receptor type tyrosine kinase family of proteins. Fyn is involved in the control of cell growth and is required in the following pathways: T and B cell receptor signaling, integrin-mediated signaling, growth factor and cytokine receptor signaling, platelet activation, ion channel function, cell adhesion, axon guidance, fertilization, entry into mitosis, and differentiation of natural killer cells, oligodendrocytes and keratinocytes. The protein associates with the p85 subunit of phosphatidylinositol 3-kinase and interacts with the Fyn-binding protein. Alternatively spliced transcript variants encoding distinct isoforms exist. Fyn is primarily localized to the cytoplasmic leaflet of the plasma membrane. Tyrosine phosphorylation of target proteins by Fyn serves to either regulate target protein activity, and/or to generate a binding site on the target protein that recruits other signaling molecules. FYN has been shown to interact with a number of proteins including: BCAR1, Cbl, Janus kinase, nephrin, Sky, tyrosine kinase, Wiskott-Aldrich syndrome protein, and Zap-70. Fyn has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAE-ELLQLPDTKvGSFMIRESETKKGFYSLSVRH------RQVKHYRIFRLPNNWYYISPRLTFQCLEDL 173
Cdd:cd10368    5 WYFGKLGRKDAErQLLSFGNPR-GTFLIRESETTKGAYSLSIRDwddmkgDHVKHYKIRKLDNGGYYITTRAQFETLQQL 83

                         90
                 ....*....|....*...
gi 194328725 174 VNHYSEVADGLCCVLTTP 191
Cdd:cd10368   84 VQHYSETANGLCKVLIVT 101

SH2 domain;

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 194328725  101 WLFEGLGRDKAEELLqLPDTKVGSFMIRESETKKGFYSLSVRHR-QVKHYRIFRLPNNWYYISPRLTFQCLEDLVNHY 177
Cdd:pfam00017   1 WYHGKISRQEAERLL-LNGKPDGTFLVRESESTPGGYTLSVRDDgKVKHYKIQSTDNGGYYISGGVKFSSLAELVEHY 77

Src homology 2 (SH2) domain found in the Src oncogene at 42A (Src42); Src42 is a member of the Src non-receptor type tyrosine kinase family of proteins. The integration of receptor tyrosine kinase-induced RAS and Src42 signals by Connector eNhancer of KSR (CNK) as a two-component input is essential for RAF activation in Drosophila. Src42 is present in a wide variety of organisms including: California sea hare, pea aphid, yellow fever mosquito, honey bee, Panamanian leafcutter ant, and sea urchin. Src42 has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. Like the other members of the Src family the SH2 domain in addition to binding the target, also plays an autoinhibitory role by binding to its C-terminal tail. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRH-RQVKHYRIFRLPNNWYYISPRLTFQCLEDLVNHYSE 179
Cdd:cd10370    5 WYFGKIKRIEAEKKLLLPENEHGAFLIRDSESRHNDYSLSVRDgDTVKHYRIRQLDEGGFFIARRTTFRTLQELVEHYSK 84

                         90
                 ....*....|..
gi 194328725 180 VADGLCCVLTTP 191
Cdd:cd10370   85 DSDGLCVNLRKP 96

Src homology 2 (SH2) domain found in the Fyn-related kinase (Frk); Frk is a member of the Src non-receptor type tyrosine kinase family of proteins. The Frk subfamily is composed of Frk/Rak and Iyk/Bsk/Gst. It is expressed primarily epithelial cells. Frk is a nuclear protein and may function during G1 and S phase of the cell cycle and suppress growth. Unlike the other Src members it lacks a glycine at position 2 of SH4 which is important for addition of a myristic acid moiety that is involved in targeting Src PTKs to cellular membranes. FRK and SHB exert similar effects when overexpressed in rat phaeochromocytoma (PC12) and beta-cells, where both induce PC12 cell differentiation and beta-cell proliferation. Under conditions that cause beta-cell degeneration these proteins augment beta-cell apoptosis. The FRK-SHB responses involve FAK and insulin receptor substrates (IRS) -1 and -2. Frk has been demonstrated to interact with retinoblastoma protein. Frk regulates PTEN protein stability by phosphorylating PTEN, which in turn prevents PTEN degradation. Frk also plays a role in regulation of embryonal pancreatic beta cell formation. Frk has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. Like the other members of the Src family the SH2 domain in addition to binding the target, also plays an autoinhibitory role by binding to its activation loop. The tryosine involved is at the same site as the tyrosine involved in the autophosphorylation of Src. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRHRQ-VKHYRIFRLPNNWYYISPRLTFQCLEDLVNHYSE 179
Cdd:cd10369    5 WFFGAIKRADAEKQLLYSENQTGAFLIRESESQKGEFSLSVLDGGvVKHYRIRRLDEGGFFLTRRKTFSTLNEFVNYYTT 84

                         90
                 ....*....|..
gi 194328725 180 VADGLCCVLTTP 191
Cdd:cd10369   85 TSDGLCVKLGKP 96

Src homology 2 (SH2) domain found in tyrosine kinase sarcoma (Src); Src is a member of the Src non-receptor type tyrosine kinase family of proteins. Src is thought to play a role in the regulation of embryonic development and cell growth. Members here include v-Src and c-Src. v-Src lacks the C-terminal inhibitory phosphorylation site and is therefore constitutively active as opposed to normal cellular src (c-Src) which is only activated under certain circumstances where it is required (e.g. growth factor signaling). v-Src is an oncogene whereas c-Src is a proto-oncogene. c-Src consists of three domains, an N-terminal SH3 domain, a central SH2 domain and a tyrosine kinase domain. The SH2 and SH3 domains work together in the auto-inhibition of the kinase domain. The phosphorylation of an inhibitory tyrosine near the c-terminus of the protein produces a binding site for the SH2 domain which then facilitates binding of the SH3 domain to a polyproline site within the linker between the SH2 domain and the kinase domain. Binding of the SH3 domain inactivates the enzyme. This allows for multiple mechanisms for c-Src activation: dephosphorylation of the C-terminal tyrosine by a protein tyrosine phosphatase, binding of the SH2 domain by a competitive phospho-tyrosine residue, or competitive binding of a polyproline binding site to the SH3 domain. Unlike most other Src members Src lacks cysteine residues in the SH4 domain that undergo palmitylation. Serine and threonine phosphorylation sites have also been identified in the unique domains of Src and are believed to modulate protein-protein interactions or regulate catalytic activity. Alternatively spliced forms of Src, which contain 6- or 11-amino acid insertions in the SH3 domain, are expressed in CNS neurons. c-Src has a unique N-terminal domain, an SH3 domain, an SH2 domain, a kinase domain and a regulatory tail, as do the other members of the family. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSV------RHRQVKHYRIFRLPNNWYYISPRLTFQCLEDLV 174
Cdd:cd10365    5 WYFGKITRRESERLLLNAENPRGTFLVRESETTKGAYCLSVsdfdnaKGLNVKHYKIRKLDSGGFYITSRTQFNSLQQLV 84

                         90
                 ....*....|....*.
gi 194328725 175 NHYSEVADGLCCVLTT 190
Cdd:cd10365   85 AYYSKHADGLCHRLTT 100

Src homology 2 (SH2) domain; In general, SH2 domains are involved in signal transduction; they bind pTyr-containing polypeptide ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites. They are present in a wide array of proteins including: adaptor proteins (Nck1, Crk, Grb2), scaffolds (Slp76, Shc, Dapp1), kinases (Src, Syk, Fps, Tec), phosphatases (Shp-1, Shp-2), transcription factors (STAT1), Ras signaling molecules (Ras-Gap), ubiquitination factors (c-Cbl), cytoskeleton regulators (Tensin), signal regulators (SAP), and phospholipid second messengers (PLCgamma), amongst others.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQlpDTKVGSFMIRESETKKGFYSLSVRH--RQVKHYRIFRLPNNWYYI-SPRLTFQCLEDLVNHY 177
Cdd:cd00173    2 WFHGSISREEAERLLR--GKPDGTFLVRESSSEPGDYVLSVRSgdGKVKHYLIERNEGGYYLLgGSGRTFPSLPELVEHY 79

Src homology 2 (SH2) domain found in Carboxyl-Terminal Src Kinase (Csk); Both the C-terminal Src kinase (CSK) and CSK-homologous kinase (CHK) are members of the CSK-family of protein tyrosine kinases. These proteins suppress activity of Src-family kinases (SFK) by selectively phosphorylating the conserved C-terminal tail regulatory tyrosine by a similar mechanism. CHK is also capable of inhibiting SFKs by a non-catalytic mechanism that involves binding of CHK to SFKs to form stable protein complexes. The unphosphorylated form of SFKs is inhibited by CSK and CHK by a two-step mechanism. The first step involves the formation of a complex of SFKs with CSK/CHK with the SFKs in the complex are inactive. The second step, involves the phosphorylation of the C-terminal tail tyrosine of SFKs, which then dissociates and adopt an inactive conformation. The structural basis of how the phosphorylated SFKs dissociate from CSK/CHK to adopt the inactive conformation is not known. The inactive conformation of SFKs is stabilized by two intramolecular inhibitory interactions: (a) the pYT:SH2 interaction in which the phosphorylated C-terminal tail tyrosine (YT) binds to the SH2 domain, and (b) the linker:SH3 interaction of which the SH2-kinase domain linker binds to the SH3 domain. SFKs are activated by multiple mechanisms including binding of the ligands to the SH2 and SH3 domains to displace the two inhibitory intramolecular interactions, autophosphorylation, and dephosphorylation of YT. By selective phosphorylation and the non-catalytic inhibitory mechanism CSK and CHK are able to inhibit the active forms of SFKs. CSK and CHK are regulated by phosphorylation and inter-domain interactions. They both contain SH3, SH2, and kinase domains separated by the SH3-SH2 connector and SH2 kinase linker, intervening segments separating the three domains. They lack a conserved tyrosine phosphorylation site in the kinase domain and the C-terminal tail regulatory tyrosine phosphorylation site. The CSK SH2 domain is crucial for stabilizing the kinase domain in the active conformation. A disulfide bond here regulates CSK kinase activity. The subcellular localization and activity of CSK are regulated by its SH2 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPdtKVGSFMIRESETKKGFYSLSVR-HRQVKHYRIfrlpnnwYYISPRLT------FQCLEDL 173
Cdd:cd09937    5 WFHGKISREEAERLLQPP--EDGLFLVRESTNYPGDYTLCVSfEGKVEHYRV-------IYRNGKLTideeeyFENLIQL 75

                         90
                 ....*....|....*...
gi 194328725 174 VNHYSEVADGLCCVLTTP 191
Cdd:cd09937   76 VEHYTKDADGLCTRLVKP 93

C-terminal Src homology 2 (C-SH2) domain found in SH2 domain Phosphatases (SHP) proteins; The SH2 domain phosphatases (SHP-1, SHP-2/Syp, Drosophila corkscrew (csw), and Caenorhabditis elegans Protein Tyrosine Phosphatase (Ptp-2)) are cytoplasmic signaling enzymes. They are both targeted and regulated by interactions of their SH2 domains with phosphotyrosine docking sites. These proteins contain two SH2 domains (N-SH2, C-SH2) followed by a tyrosine phosphatase (PTP) domain, and a C-terminal extension. Shp1 and Shp2 have two tyrosyl phosphorylation sites in their C-tails, which are phosphorylated differentially by receptor and nonreceptor PTKs. Csw retains the proximal tyrosine and Ptp-2 lacks both sites. Shp-binding proteins include receptors, scaffolding adapters, and inhibitory receptors. Some of these bind both Shp1 and Shp2 while others bind only one. Most proteins that bind a Shp SH2 domain contain one or more immuno-receptor tyrosine-based inhibitory motifs (ITIMs): [SIVL]xpYxx[IVL]. Shp1 N-SH2 domain blocks the catalytic domain and keeps the enzyme in the inactive conformation, and is thus believed to regulate the phosphatase activity of SHP-1. Its C-SH2 domain is thought to be involved in searching for phosphotyrosine activators. The SHP2 N-SH2 domain is a conformational switch; it either binds and inhibits the phosphatase, or it binds phosphoproteins and activates the enzyme. The C-SH2 domain contributes binding energy and specificity, but it does not have a direct role in activation. Csw SH2 domain function is essential, but either SH2 domain can fulfill this requirement. The role of the csw SH2 domains during Sevenless receptor tyrosine kinase (SEV) signaling is to bind Daughter of Sevenless rather than activated SEV. Ptp-2 acts in oocytes downstream of sheath/oocyte gap junctions to promote major sperm protein (MSP)-induced MAP Kinase (MPK-1) phosphorylation. Ptp-2 functions in the oocyte cytoplasm, not at the cell surface to inhibit multiple RasGAPs, resulting in sustained Ras activation. It is thought that MSP triggers PTP-2/Ras activation and ROS production to stimulate MPK-1 activity essential for oocyte maturation and that secreted MSP domains and Cu/Zn superoxide dismutases function antagonistically to control ROS and MAPK signaling. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  96 RVYHGWLfegLGRDkAEELLQlPDTKVGSFMIRESETKKGFYSLSVR--HRQVKHYRIfRLPNNWYYISPRLTFQCLEDL 173
Cdd:cd09931    1 RWFHGHL---SGKE-AEKLLL-EKGKPGSFLVRESQSKPGDFVLSVRtdDDKVTHIMI-RCQGGKYDVGGGEEFDSLTDL 74

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 194328725 174 VNHYSEVadglccvlttpcltqstaaPAVRASSSPVTLRQ 213
Cdd:cd09931   75 VEHYKKN-------------------PMVETSGTVVHLKQ 95

N-terminal Src homology 2 (SH2) domain found in SH2 domains, ANK, and kinase domain (shark) proteins; These non-receptor protein-tyrosine kinases contain two SH2 domains, five ankyrin (ANK)-like repeats, and a potential tyrosine phosphorylation site in the carboxyl-terminal tail which resembles the phosphorylation site in members of the src family. Like, mammalian non-receptor protein-tyrosine kinases, ZAP-70 and syk proteins, they do not have SH3 domains. However, the presence of ANK makes these unique among protein-tyrosine kinases. Both tyrosine kinases and ANK repeats have been shown to transduce developmental signals, and SH2 domains are known to participate intimately in tyrosine kinase signaling. These tyrosine kinases are believed to be involved in epithelial cell polarity. The members of this family include the shark (SH2 domains, ANK, and kinase domain) gene in Drosophila and yellow fever mosquitos, as well as the hydra protein HTK16. Drosophila Shark is proposed to transduce intracellularly the Crumbs, a protein necessary for proper organization of ectodermal epithelia, intercellular signal. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  96 RVYHGwlfeGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRHR-QVKHYRIFRLPNNWYYIS-PRLTFQCLEDL 173
Cdd:cd10347    2 RWYHG----KISREVAEALLLREGGRDGLFLVRESTSAPGDYVLSLLAQgEVLHYQIRRHGEDAFFSDdGPLIFHGLDTL 77

                 ....
gi 194328725 174 VNHY 177
Cdd:cd10347   78 IEHY 81

C-terminal Src homology 2 (SH2) domain found in Ras GTPase-activating protein 1 (GAP); RasGAP is part of the GAP1 family of GTPase-activating proteins. The protein is located in the cytoplasm and stimulates the GTPase activity of normal RAS p21, but not its oncogenic counterpart. Acting as a suppressor of RAS function, the protein enhances the weak intrinsic GTPase activity of RAS proteins resulting in RAS inactivation, thereby allowing control of cellular proliferation and differentiation. Mutations leading to changes in the binding sites of either protein are associated with basal cell carcinomas. Alternative splicing results in two isoforms. The shorter isoform which lacks the N-terminal hydrophobic region, has the same activity, and is expressed in placental tissues. In general longer isoform contains 2 SH2 domains, a SH3 domain, a pleckstrin homology (PH) domain, and a calcium-dependent phospholipid-binding C2 domain. The C-terminus contains the catalytic domain of RasGap which catalyzes the activation of Ras by hydrolyzing GTP-bound active Ras into an inactive GDP-bound form of Ras. This model contains the C-terminal SH2 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 194328725 101 WLFEGLGRDKAEELLqLPDTKVGSFMIRESETKKGFYSLSVR-HRQVKHYRIFRLPNNWYYISPRlTFQCLEDLVNHY 177
Cdd:cd10354    2 WFHGKISREEAYNML-VKVGGPGSFLVRESDNTPGDYSLSFRvNEGIKHFKIIPTGNNQFMMGGR-YFSSLDDVIDRY 77

N-terminal Src homology 2 (N-SH2) domain in Phospholipase C gamma; Phospholipase C gamma is a signaling molecule that is recruited to the C-terminal tail of the receptor upon autophosphorylation of a highly conserved tyrosine. PLCgamma is composed of a Pleckstrin homology (PH) domain followed by an elongation factor (EF) domain, 2 catalytic regions of PLC domains that flank 2 tandem SH2 domains (N-SH2, C-SH2), and ending with a SH3 domain and C2 domain. N-SH2 SH2 domain-mediated interactions represent a crucial step in transmembrane signaling by receptor tyrosine kinases. SH2 domains recognize phosphotyrosine (pY) in the context of particular sequence motifs in receptor phosphorylation sites. Both N-SH2 and C-SH2 have a very similar binding affinity to pY. But in growth factor stimulated cells these domains bind to different target proteins. N-SH2 binds to pY containing sites in the C-terminal tails of tyrosine kinases and other receptors. Recently it has been shown that this interaction is mediated by phosphorylation-independent interactions between a secondary binding site found exclusively on the N-SH2 domain and a region of the FGFR1 tyrosine kinase domain. This secondary site on the SH2 cooperates with the canonical pY site to regulate selectivity in mediating a specific cellular process. C-SH2 binds to an intramolecular site on PLCgamma itself which allows it to hydrolyze phosphatidylinositol-4,5-bisphosphate into diacylglycerol and inositol triphosphate. These then activate protein kinase C and release calcium. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  98 YHGWLFEGlgRDKAEELLQ----LPDtkvGSFMIRESETKKGFYSLSVRHR-QVKHYRIFRLPNNW---YYISPRLTFQC 169
Cdd:cd10341    7 FHGKLGDG--RDEAEKLLLeyceGGD---GTFLVRESETFVGDYTLSFWRNgKVQHCRIRSRQENGekkYYLTDNLVFDS 81

                         90
                 ....*....|.
gi 194328725 170 LEDLVNHYSEV 180
Cdd:cd10341   82 LYELIDYYRQN 92

Src homology 2 (SH2) domain found in feline sarcoma, Fujinami poultry sarcoma, and fes-related (Fes/Fps/Fer) proteins; The Fps family consists of members Fps/Fes and Fer/Flk/Tyk3. They are cytoplasmic protein-tyrosine kinases implicated in signaling downstream from cytokines, growth factors and immune receptors. Fes/Fps/Fer contains three coiled-coil regions, an SH2 (Src-homology-2) and a TK (tyrosine kinase catalytic) domain signature. Members here include: Fps/Fes, Fer, Kin-31, and In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  98 YHGWLfeglGRDKAEELLQlpdtKVGSFMIRESETK---KGFYSLSVRHR-QVKHYRIFRLPNNWYYISPRlTFQCLEDL 173
Cdd:cd10361    9 YHGLL----PREDAEELLK----NDGDFLVRKTEPKgggKRKLVLSVRWDgKIRHFVINRDDGGKYYIEGK-SFKSISEL 79

                 ....
gi 194328725 174 VNHY 177
Cdd:cd10361   80 INYY 83

Src homology 2 (SH2) domain found in alpha2-chimerin and beta2-chimerin proteins; Chimerins are a family of phorbol ester- and diacylglycerol-responsive GTPase-activating proteins. Alpha1-chimerin (formerly known as n-chimerin) and alpha2-chimerin are alternatively spliced products of a single gene, as are beta1- and beta2-chimerin. alpha1- and beta1-chimerin have a relatively short N-terminal region that does not encode any recognizable domains, whereas alpha2- and beta2-chimerin both include a functional SH2 domain that can bind to phosphotyrosine motifs within receptors. All of the isoforms contain a GAP domain with specificity in vitro for Rac1 and a diacylglycerol (DAG)-binding C1 domain which allows them to translocate to membranes in response to DAG signaling and anchors them in close proximity to activated Rac. Other C1 domain-containing diacylglycerol receptors including: PKC, Munc-13 proteins, phorbol ester binding scaffolding proteins involved in Ca2+-stimulated exocytosis, and RasGRPs, diacylglycerol-activated guanine-nucleotide exchange factors (GEFs) for Ras and Rap1. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  98 YHGwlfeGLGRDKAEELLQlpDTKVGSFMIRESETKKGFYSLSVR-HRQVKHYRIFRLPNNWYYISPRLTFQCLEDLvnh 176
Cdd:cd10352    9 YHG----LISREEAEQLLS--GASDGSYLIRESSRDDGYYTLSLRfNGKVKNYKLYYDGKNHYHYVGEKRFDTIHDL--- 79

                 ....*...
gi 194328725 177 yseVADGL 184
Cdd:cd10352   80 ---VADGL 84

Src homology 3 domain of Blk Protein Tyrosine Kinase; Blk is a member of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. It is expressed specifically in B-cells and is involved in pre-BCR (B-cell receptor) signaling. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 194328725  43 FLAVLSDYPSPDISPPIFRRGEKLRVISDEGGWWKAISLSTGRESYIPGICVAR 96
Cdd:cd12009    1 CVIAQYDFVPSNERDLQLKKGEKLQVLKSDGEWWLAKSLTTGKEGYIPSNYVAR 54

C-terminal Src homology 2 (C-SH2) domain in Phospholipase C gamma; Phospholipase C gamma is a signaling molecule that is recruited to the C-terminal tail of the receptor upon autophosphorylation of a highly conserved tyrosine. PLCgamma is composed of a Pleckstrin homology (PH) domain followed by an elongation factor (EF) domain, 2 catalytic regions of PLC domains that flank 2 tandem SH2 domains (N-SH2, C-SH2), and ending with a SH3 domain and C2 domain. N-SH2 SH2 domain-mediated interactions represent a crucial step in transmembrane signaling by receptor tyrosine kinases. SH2 domains recognize phosphotyrosine (pY) in the context of particular sequence motifs in receptor phosphorylation sites. Both N-SH2 and C-SH2 have a very similar binding affinity to pY. But in growth factor stimulated cells these domains bind to different target proteins. N-SH2 binds to pY containing sites in the C-terminal tails of tyrosine kinases and other receptors. Recently it has been shown that this interaction is mediated by phosphorylation-independent interactions between a secondary binding site found exclusively on the N-SH2 domain and a region of the FGFR1 tyrosine kinase domain. This secondary site on the SH2 cooperates with the canonical pY site to regulate selectivity in mediating a specific cellular process. C-SH2 binds to an intramolecular site on PLCgamma itself which allows it to hydrolyze phosphatidylinositol-4,5-bisphosphate into diacylglycerol and inositol triphosphate. These then activate protein kinase C and release calcium. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELL-QLPdtKVGSFMIRESETKKGFYSLSVR-HRQVKHYRIF---RLpnnwyYISPRLTFQCLEDLVN 175
Cdd:cd09932    6 WFHANLTREQAEEMLmRVP--RDGAFLVRPSETDPNSFAISFRaEGKIKHCRIKqegRL-----FVIGTSQFESLVELVS 78

                 ...
gi 194328725 176 HYS 178
Cdd:cd09932   79 YYE 81

Src homology 2 (SH2) domain found in Tec protein, Txk; A member of the Tec protein tyrosine kinase Txk is expressed in thymus, spleen, lymph node, T lymphocytes, NK cells, mast cell lines, and myeloid cell line. Txk plays a role in TCR signal transduction, T cell development, and selection which is analogous to the function of Itk. Txk has been shown to interact with IFN-gamma. Unlike most of the Tec family members Txk lacks a PH domain. Instead Txk has a unique region containing a palmitoylated cysteine string which has a similar membrane tethering function as the PH domain. Txk also has a zinc-binding motif, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP and crucial to the function of the PH domain. It is not present in Txk which is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homolog also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQlPDTKVGSFMIRESeTKKGFYSLSV-----RHRQ--VKHYRIFRLPNNWYYISPRLTFQCLEDL 173
Cdd:cd10398    8 WYHKNITRNQAERLLR-QESKEGAFIVRDS-RHLGSYTISVftrarRSTEasIKHYQIKKNDSGQWYVAERHLFQSIPEL 85

                         90
                 ....*....|....*...
gi 194328725 174 VNHYSEVADGLCCVLTTP 191
Cdd:cd10398   86 IQYHQHNAAGLMSRLRYP 103

Src homology 2 (SH2) domain found in Tec protein, Bmx; A member of the Tec protein tyrosine kinase Bmx is expressed in the endothelium of large arteries, fetal endocardium, adult endocardium of the left ventricle, bone marrow, lung, testis, granulocytes, myeloid cell lines, and prostate cell lines. Bmx is involved in the regulation of Rho and serum response factor (SRF). Bmx has been shown to interact with PAK1, PTK2, PTPN21, and RUFY1. Most of the Tec family members have a PH domain (Txk and the short (type 1) splice variant of Drosophila Btk29A are exceptions), a Tec homology (TH) domain, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP. It is crucial for the function of Tec PH domains. It is not present in Txk and the type 1 splice form of the Drosophila homolog. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 100 GWLFEGLGRDKAEELLQlPDTKVGSFMIRESeTKKGFYSLSV---RHRQ----VKHYRIFRLPNNWYYISPRLTFQCLED 172
Cdd:cd10399    7 DWFAGNISRSQSEQLLR-QKGKEGAFMVRNS-SQVGMYTVSLfskAVNDkkgtVKHYHVHTNAENKLYLAENYCFDSIPK 84

                         90       100
                 ....*....|....*....|..
gi 194328725 173 LVNHYSEVADGLCCVLTTPCLT 194
Cdd:cd10399   85 LIHYHQHNSAGMITRLRHPVST 106

Src homology 3 domain of Src kinase-like Protein Tyrosine Kinases; Src subfamily members include Src, Lck, Hck, Blk, Lyn, Fgr, Fyn, Yrk, Yes, and Brk. Src (or c-Src) proteins are cytoplasmic (or non-receptor) PTKs which are anchored to the plasma membrane. They contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). However, Brk lacks the N-terminal myristoylation sites. Src proteins are involved in signaling pathways that regulate cytokine and growth factor responses, cytoskeleton dynamics, cell proliferation, survival, and differentiation. They were identified as the first proto-oncogene products, and they regulate cell adhesion, invasion, and motility in cancer cells, and tumor vasculature, contributing to cancer progression and metastasis. Src kinases are overexpressed in a variety of human cancers, making them attractive targets for therapy. They are also implicated in acute inflammatory responses and osteoclast function. Src, Fyn, Yes, and Yrk are widely expressed, while Blk, Lck, Hck, Fgr, Lyn, and Brk show a limited expression pattern. This subfamily also includes Drosophila Src42A, Src oncogene at 42A (also known as Dsrc41) which accumulates at sites of cell-cell or cell-matrix adhesion, and participates in Drosphila development and wound healing. It has been shown to promote tube elongation in the tracheal system, is essential for proper cell-cell matching during dorsal closure, and regulates cell-cell contacts in developing Drosophila eyes. The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30
                 ....*....|....*....|....*....|..
gi 194328725  60 FRRGEKLRVISD-EGGWWKAISLSTGRESYIP 90
Cdd:cd11845   18 FKKGDRLQILDDsDGDWWLARHLSTGKEGYIP 49

Src homology 2 (SH2) domain found in Tec protein, Bruton's tyrosine kinase (Btk); A member of the Tec protein tyrosine kinase Btk is expressed in bone marrow, spleen, all hematopoietic cells except T lymphocytes and plasma cells where it plays a crucial role in B cell maturation and mast cell activation. Btk has been shown to interact with GNAQ, PLCG2, protein kinase D1, B-cell linker, SH3BP5, caveolin 1, ARID3A, and GTF2I. Most of the Tec family members have a PH domain (Txk and the short (type 1) splice variant of Drosophila Btk29A are exceptions), a Tec homology (TH) domain, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. Btk is implicated in the primary immunodeficiency disease X-linked agammaglobulinemia (Bruton's agammaglobulinemia). The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP. It is crucial for the function of Tec PH domains and it's lack of presence in Txk is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homolog also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. Two tyrosine phosphorylation (pY) sites have been identified in Btk: one located in the activation loop of the catalytic domain which regulates the transition between open (active) and closed (inactive) states and the other in its SH3 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDtKVGSFMIRESeTKKGFYSLSVRHR-------QVKHYRIFRLPNNWYYISPRLTFQCLEDL 173
Cdd:cd10397    8 WYSKNMTRSQAEQLLKQEG-KEGGFIVRDS-SKAGKYTVSVFAKsagdpqgVIRHYVVCSTPQSQYYLAEKHLFSTIPEL 85

                         90
                 ....*....|....*...
gi 194328725 174 VNHYSEVADGLCCVLTTP 191
Cdd:cd10397   86 INYHQHNAAGLISRLKYP 103

N-terminal Src homology 2 (SH2) domain found in Ras GTPase-activating protein 1 (GAP); RasGAP is part of the GAP1 family of GTPase-activating proteins. The protein is located in the cytoplasm and stimulates the GTPase activity of normal RAS p21, but not its oncogenic counterpart. Acting as a suppressor of RAS function, the protein enhances the weak intrinsic GTPase activity of RAS proteins resulting in RAS inactivation, thereby allowing control of cellular proliferation and differentiation. Mutations leading to changes in the binding sites of either protein are associated with basal cell carcinomas. Alternative splicing results in two isoforms. The shorter isoform which lacks the N-terminal hydrophobic region, has the same activity, and is expressed in placental tissues. In general the longer isoform contains 2 SH2 domains, a SH3 domain, a pleckstrin homology (PH) domain, and a calcium-dependent phospholipid-binding C2 domain. The C-terminus contains the catalytic domain of RasGap which catalyzes the activation of Ras by hydrolyzing GTP-bound active Ras into an inactive GDP-bound form of Ras. This model contains the N-terminal SH2 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  98 YHGwlfeGLGRDKAEELLQlPDTKVGSFMIRESETKKGFYSLS-VRHRQVKHYRIFRLPNNwYYISPRlTFQCLEDLVNH 176
Cdd:cd10353   22 YHG----RLDRTIAEERLR-QAGKLGSYLIRESDRRPGSFVLSfLSRTGVNHFRIIAMCGD-YYIGGR-RFSSLSDLIGY 94

                 ....*...
gi 194328725 177 YSEVADGL 184
Cdd:cd10353   95 YSHVSCLL 102

Src homology 2 (SH2) domain found in the growth factor receptor bound, subclass 7 (Grb7) proteins; The Grb family binds to the epidermal growth factor receptor (EGFR, erbB1) via their SH2 domains. There are 3 members of the Grb7 family of proteins: Grb7, Grb10, and Grb14. They are composed of an N-terminal Proline-rich domain, a Ras Associating-like (RA) domain, a Pleckstrin Homology (PH) domain, a phosphotyrosine interaction region (PIR, BPS) and a C-terminal SH2 domain. The SH2 domains of Grb7, Grb10 and Grb14 preferentially bind to a different RTK. Grb7 binds strongly to the erbB2 receptor, unlike Grb10 and Grb14 which bind weakly to it. Grb14 binds to Fibroblast Growth Factor Receptor (FGFR). Grb10 has been shown to interact with many different proteins, including the insulin and IGF1 receptors, platelet-derived growth factor (PDGF) receptor-beta, Ret, Kit, Raf1 and MEK1, and Nedd4. Grb7 family proteins are phosphorylated on serine/threonine as well as tyrosine residues. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQLPDTKVGSFMIRESETKKGFYSLSVRHRQ-VKHYRIFRL--PNNWYYI--SPRLTFQCLEDLVN 175
Cdd:cd09944    7 WFHGGISRDEAARLIRQQGLVDGVFLVRESQSNPGAFVLSLKHGQkIKHYQIIPIedEGQWYFTldDGVTKFYDLLQLVE 86

                         90
                 ....*....|....*..
gi 194328725 176 HYSEVADGLCCVLTTPC 192
Cdd:cd09944   87 FYQLNAGSLPTRLKHYC 103

Src homology 3 domain of Fyn and Yrk Protein Tyrosine Kinases; Fyn and Yrk (Yes-related kinase) are members of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. Fyn, together with Lck, plays a critical role in T-cell signal transduction by phosphorylating ITAM (immunoreceptor tyr activation motif) sequences on T-cell receptors, ultimately leading to the proliferation and differentiation of T-cells. In addition, Fyn is involved in the myelination of neurons, and is implicated in Alzheimer's and Parkinson's diseases. Yrk has been detected only in chickens. It is primarily found in neuronal and epithelial cells and in macrophages. It may play a role in inflammation and in response to injury. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|
gi 194328725  47 LSDYPSPDISPPIFRRGEKLRVI-SDEGGWWKAISLSTGRESYIPGICVA 95
Cdd:cd12006    6 LYDYEARTEDDLSFHKGEKFQILnSSEGDWWEARSLTTGETGYIPSNYVA 55

C-terminal Src homology 2 (cSH2) domain found in p85; Phosphoinositide 3-kinases (PI3Ks) are essential for cell growth, migration, and survival. p110, the catalytic subunit, is composed of an adaptor-binding domain, a Ras-binding domain, a C2 domain, a helical domain, and a kinase domain. The regulatory unit is called p85 and is composed of an SH3 domain, a RhoGap domain, a N-terminal SH2 (nSH2) domain, a inter SH2 (iSH2) domain, and C-terminal (cSH2) domain. There are 2 inhibitory interactions between p110alpha and p85 of P13K: 1) p85 nSH2 domain with the C2, helical, and kinase domains of p110alpha and 2) p85 iSH2 domain with C2 domain of p110alpha. There are 3 inhibitory interactions between p110beta and p85 of P13K: 1) p85 nSH2 domain with the C2, helical, and kinase domains of p110beta, 2) p85 iSH2 domain with C2 domain of p110alpha, and 3) p85 cSH2 domain with the kinase domain of p110alpha. It is interesting to note that p110beta is oncogenic as a wild type protein while p110alpha lacks this ability. One explanation is the idea that the regulation of p110beta by p85 is unique because of the addition of inhibitory contacts from the cSH2 domain and the loss of contacts in the iSH2 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725 101 WLFEGLGRDKAEELLQ-LPDtkvGSFMIRESETKkGFYSLSVR-HRQVKHYRIFRLPNNWYYISPRLTFQCLEDLVNHYS 178
Cdd:cd09930    8 WLVGDINRTQAEELLRgKPD---GTFLIRESSTQ-GCYACSVVcNGEVKHCVIYKTETGYGFAEPYNLYESLKELVLHYA 83

Src homology 2 domain found in SH2 domain-containing adapter proteins B, D, E, and F (SHB, SHD, SHE, SHF); SHB, SHD, SHE, and SHF are SH2 domain-containing proteins that play various roles throughout the cell. SHB functions in generating signaling compounds in response to tyrosine kinase activation. SHB contains proline-rich motifs, a phosphotyrosine binding (PTB) domain, tyrosine phosphorylation sites, and a SH2 domain. SHB mediates certain aspects of platelet-derived growth factor (PDGF) receptor-, fibroblast growth factor (FGF) receptor-, neural growth factor (NGF) receptor TRKA-, T cell receptor-, interleukin-2 (IL-2) receptor- and focal adhesion kinase- (FAK) signaling. SRC-like FYN-Related Kinase FRK/RAK (also named BSK/IYK or GTK) and SHB regulate apoptosis, proliferation and differentiation. SHB promotes apoptosis and is also required for proper mitogenicity, spreading and tubular morphogenesis in endothelial cells. SHB also plays a role in preventing early cavitation of embryoid bodies and reduces differentiation to cells expressing albumin, amylase, insulin and glucagon. SHB is a multifunctional protein that has difference responses in different cells under various conditions. SHE is expressed in heart, lung, brain, and skeletal muscle, while expression of SHD is restricted to the brain. SHF is mainly expressed in skeletal muscle, brain, liver, prostate, testis, ovary, small intestine, and colon. SHD may be a physiological substrate of c-Abl and may function as an adapter protein in the central nervous system. It is also thought to be involved in apoptotic regulation. SHD contains five YXXP motifs, a substrate sequence preferred by Abl tyrosine kinases, in addition to a poly-proline rich region and a C-terminal SH2 domain. SHE contains two pTry protein binding domains, protein interaction domain (PID) and a SH2 domain, followed by a glycine-proline rich region, all of which are N-terminal to the phosphotyrosine binding (PTB) domain. SHF contains four putative tyrosine phosphorylation sites and an SH2 domain. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 194328725  98 YHGwlfeGLGRDKAEELLQLpdTKVGSFMIRESETKKGFYSLSVRHRQ-VKHYRIFRLPNNWYYI---SPrlTFQCLEDL 173
Cdd:cd09945    4 YHG----AITRIEAESLLRP--CKEGSYLVRNSESTKQDYSLSLKSAKgFMHMRIQRNETGQYILgqfSR--PFETIPEM 75

                 ....*
gi 194328725 174 VNHYS 178
Cdd:cd09945   76 IRHYC 80