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Bud4 Pleckstrin homology (PH) domain Bud4 is an anillin-like yeast protein involved in the formation and the disassembly of the double ring structure formed by the septins during cytokinesis. Bud4 acts with Bud3 and and in parallel with septin phosphorylation by the p21-activated kinase Cla4 and the septin-dependent kinase Gin4. Bud4 is regulated by the cyclin-dependent protein kinase Cdk1, the master regulator of cell cycle progression. Bud4 contains an anillin-like domain followed by a PH domain. In addition there are two consensus Cdk phosphorylation sites: one at the N-terminus and one right before the C-terminal PH domain. Anillins also have C-terminal PH domains. 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.",