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A-kinase anchoring protein 13 Pleckstrin homology (PH) domain The Rho-specific GEF activity of AKAP13 (also called Brx-1, AKAP-Lbc, and proto-Lbc) mediates signaling downstream of G-protein coupled receptors and Toll-like receptor 2. It plays a role in cell growth, cell development and actin fiber formation. Protein kinase A (PKA) binds and phosphorylates AKAP13, regulating its Rho-GEF activity. Alternative splicing of this gene in humans has at least 3 transcript variants encoding different isoforms (i.e. proto-/onco-Lymphoid blast crisis, Lbc and breast cancer nuclear receptor-binding auxiliary protein, Brx) containing a dbl oncogene homology (DH) domain and PH domain which are required for full transforming activity. The DH domain is associated with guanine nucleotide exchange activation while the PH domain has multiple functions including determine protein sub-cellular localisation via phosphoinositide interactions, while others bind protein partners. Other ligands include protein kinase C which is bound by the PH domain of AKAP13, serving to activate protein kinase D and mobilize a cardiac hypertrophy signaling pathway. 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.",