Engulfment and cell motility protein 1 pleckstrin homology (PH) domain
DOCK2 (Dedicator of cytokinesis 2), a hematopoietic cell-specific, atypical GEF, controls lymphocyte migration through Rac activation. A DOCK2-ELMO1 complex s necessary for DOCK2-mediated Rac signaling. DOCK2 contains a SH3 domain at its N-terminus, followed by a lipid binding DHR1 domain, and a Rac-binding DHR2 domain at its C-terminus. ELMO1, a mammalian homolog of C. elegans CED-12, contains the N-terminal RhoG-binding region, the ELMO domain, the PH domain, and the C-terminal sequence with three PxxP motifs. The C-terminal region of ELMO1, including the Pro-rich sequence, binds the SH3-containing region of DOCK2 forming a intermolecular five-helix bundle along with the PH domain of ELMO1. Autoinhibition of ELMO1 and DOCK2 is accomplished by the interactions of the EID and EAD domains and SH3 and DHR2 domains, respectively. The interaction of DOCK2 and ELMO1 mutually relieve their autoinhibition and results in the activation of Rac1. The PH domain of ELMO1 does not bind phosphoinositides due to the absence of key binding residues. It more closely resembles the FERM domain rather than other PH domains. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",