ARHGAP21 and related proteins pleckstrin homology (PH) domain
ARHGAP family genes encode Rho/Rac/Cdc42-like GTPase activating proteins with a RhoGAP domain. These proteins functions as a GTPase-activating protein (GAP) for RHOA and CDC42. ARHGAP21 controls the Arp2/3 complex and F-actin dynamics at the Golgi complex by regulating the activity of the small GTPase Cdc42. It is recruited to the Golgi by to GTPase, ARF1, through its PH domain and its helical motif. It is also required for CTNNA1 recruitment to adherens junctions. ARHGAP21 and it related proteins all contains a PH domain and a RhoGAP domain. Some of the members have additional N-terminal domains including PDZ, SH3, and SPEC. The ARHGAP21 PH domain interacts with the GTPbound forms of both ARF1 and ARF6 ARF-binding domain/ArfBD. The members here include: ARHGAP15, ARHGAP21, and ARHGAP23. 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.",