GTPase Regulator Associated with Focal adhesion and related proteins Pleckstrin homology (PH) domain
This hierarchy contains GRAF family members: OPHN1/oligophrenin1, GRAF1 (also called ARHGAP26/Rho GTPase activating protein 26), GRAF2 (also called ARHGAP10/ARHGAP42), AK057372, and LOC129897, all of which are members of the APPL family. OPHN1 is a RhoGAP involved in X-linked mental retardation, epilepsy, rostral ventricular enlargement, and cerebellar hypoplasia. Affected individuals have morphological abnormalities of their brain with enlargement of the cerebral ventricles and cerebellar hypoplasia. OPHN1 negatively regulates RhoA, Cdc42, and Rac1 in neuronal and non-neuronal cells. GRAF1 sculpts the endocytic membranes of the CLIC/GEEC (clathrin-independent carriers/GPI-enriched early endosomal compartments) endocytic pathway. It strongly interacts with dynamin and inhibition of dynamin abolishes CLIC/GEEC endocytosis. GRAF2, GRAF3 and oligophrenin are likely to play similar roles during clathrin-independent endocytic events. GRAF1 mutations are linked to leukaemia. All members are composed of a N-terminal BAR-PH domain, followed by a RhoGAP domain, a proline rich region, and a C-terminal SH3 domain. 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.",