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Shape and Conjugation Deficiency 1 Pleckstrin homology (PH) domain Fission yeast Scd1 is an exchange factor for Cdc42 and an effector of Ras1, the homolog of the human H-Ras. Scd2/Bem1 mediates Cdc42 activation by binding to Scd1/Cdc24 and to Cdc42. Ras1 regulates Scd1/Cdc24/Ral1, which is a putative guanine nucleotide exchange factor for Cdc42, a member of the Rho family of Ras-like proteins. Cdc42 then activates the Shk1/Orb2 protein kinase. Scd1 interacts with Klp5 and Klp6 kinesins to mediate cytokinesis. 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.",