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Leukemia-associated Rho guanine nucleotide exchange factor Pleckstrin homology (PH) domain LARG (also called RhoGEF12) belongs to regulator of G-protein signaling (RGS) domain-containing RhoGEFs that are RhoA-selective and directly activated by the Galpha12/13 family of heterotrimeric G proteins. RhoGEFs activate Rho GTPases regulating cytoskeletal structure, gene transcription, and cell migration. LARG contains a N-terminal extension, followed by Dbl homology (DH)-PH domains which bind and catalyze the exchange of GDP for GTP on RhoA in addition to a RGS domain. The active site of RhoA adopts two distinct GDP-excluding conformations among the four unique complexes in the asymmetric unit. The LARG PH domain also contains a potential protein-docking site. LARG forms a homotetramer via its DH 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.",