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Myosin phosphatase-RhoA Interacting Protein Pleckstrin homology (PH) domain M-RIP is proposed to play a role in myosin phosphatase regulation by RhoA. M-RIP contains 2 PH domains followed by a Rho binding domain (Rho-BD), and a C-terminal myosin binding subunit (MBS) binding domain (MBS-BD). The amino terminus of M-RIP with its adjacent PH domains and polyproline motifs mediates binding to both actin and Galpha. M-RIP brings RhoA and MBS into close proximity where M-RIP can target RhoA to the myosin phosphatase complex to regulate the myosin phosphorylation state. M-RIP does this via its C-terminal coiled-coil domain which interacts with the MBS leucine zipper domain of myosin phosphatase, while its Rho-BD, directly binds RhoA in a nucleotide-independent manner. 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.",