Beta spectrin binds actin and functions as a major component of the cytoskeleton underlying cellular membranes. Beta spectrin consists of multiple spectrin repeats followed by a PH domain, which binds to inositol-1,4,5-trisphosphate. The PH domain of beta-spectrin is thought to play a role in the association of spectrin with the plasma membrane of cells. 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.
Comment:the canonical binding site is delimited by the beta1- beta2 and beta3- beta4 loops; the non-canonical binding site bordered by the beta1- beta2 and beta5- beta6 loops
Comment:loop undergoes conformational change upon IP3 binding
Jiyao W et al.(2023). "The conserved domain database in 2023.",