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Boi family Pleckstrin homology domain Yeast Boi proteins Boi1 and Boi2 are functionally redundant and important for cell growth with Boi mutants displaying defects in bud formation and in the maintenance of cell polarity.They appear to be linked to Rho-type GTPase, Cdc42 and Rho3. Boi1 and Boi2 display two-hybrid interactions with the GTP-bound ("active") form of Cdc42, while Rho3 can suppress of the lethality caused by deletion of Boi1 and Boi2. These findings suggest that Boi1 and Boi2 are targets of Cdc42 that promote cell growth in a manner that is regulated by Rho3. Boi proteins contain a N-terminal SH3 domain, followed by a SAM (sterile alpha motif) domain, a proline-rich region, which mediates binding to the second SH3 domain of Bem1, and C-terminal PH domain. The PH domain is essential for its function in cell growth and is important for localization to the bud, while the SH3 domain is needed for localization to the neck. 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.",