KIFIA and KIFIB protein pleckstrin homology (PH) domain
The kinesin-3 family motors KIFIA (Caenorhabditis elegans homolog unc-104) and KIFIB transport synaptic vesicle precursors that contain synaptic vesicle proteins, such as synaptophysin, synaptotagmin and the small GTPase RAB3A, but they do not transport organelles that contain plasma membrane proteins. They have a N-terminal motor domain, followed by a coiled-coil domain, and a C-terminal PH domain. KIF1A adopts a monomeric form in vitro, but acts as a processive dimer in vivo. KIF1B has alternatively spliced isoforms distinguished by the presence or absence of insertion sequences in the conserved amino-terminal region of the protein; this results in their different motor activities. KIF1A and KIF1B bind to RAB3 proteins through the adaptor protein mitogen-activated protein kinase (MAPK) -activating death domain (MADD; also calledDENN), which was first identified as a RAB3 guanine nucleotide exchange factor (GEF). 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.",