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SifA and kinesin-interacting protein Pleckstrin homology (PH) domain SKIP (also called PLEKHM2/Pleckstrin homology domain-containing family M member 2) is a soluble cytosolic protein that contains a RUN domain and a PH domain separated by a unstructured linker region. SKIP is a target of the Salmonella effector protein SifA and the SifA-SKIP complex regulates kinesin-1 on the bacterial vacuole. The PH domain of SKIP binds to the N-terminal region of SifA while the N-terminus of SKIP is proposed to bind the TPR domain of the kinesin light chain. The opposite side of the SKIP PH domain is proposed to bind phosphoinositides. TSifA, SKIP, SseJ, and RhoA family GTPases are also thought to promote host membrane tubulation. Recently, it was shown that the lysosomal GTPase Arl8 binds to the kinesin-1 linker SKIP and that both are required for the normal intracellular distribution of lysosomes. Interestingly, two kinesin light chain binding motifs (WD) in SKIP have now been identified to match a consensus sequence for a kinesin light chain binding site found in several proteins including calsyntenin-1/alcadein, caytaxin, and vaccinia virus A36. SKIP has also been shown to interact with Rab1A. 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.",