?
Rho-Interacting Protein Pleckstrin homology (PH) domain RIP1-RhoGDI2 was obtained in a screen for proteins that bind to wild-type RhoA. RIP2, RIP3, and RIP4 were isolated from cDNA libraries with constitutively active V14RhoA (containing the C190R mutation). RIP2 represents a novel GDP/GTP exchange factor (RhoGEF), while RIP3 (p116Rip) and RIP4 are thought to be structural proteins. RhoGEF contains a Dbl(DH)/PH region, a a zinc finger motif, a leucine-rich domain, and a coiled-coil region. The last 2 domains are thought to be involved in mediating protein-protein interactions. RIP3 is a negative regulator of RhoA signaling that inhibits, either directly or indirectly, RhoA-stimulated actomyosin contractility. In plants RIP3 is localized at microtubules and interacts with the kinesin-13 family member AtKinesin-13A, suggesting a role for RIP3 in microtubule reorganization and a possible function in Rho proteins of plants (ROP)-regulated polar growth. It has a PH domain, two proline-rich regions which are putative binding sites for SH3 domains, and a COOH-terminal coiled-coil region which overlaps with the RhoA-binding region. 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.",