Kinesin-like protein KIF3B is a protein that in humans is encoded by the KIF3B gene.[5][6] KIF3B is an N-type protein that complexes with two other kinesin proteins to form two-headed anterograde motors.[7] First, KIF3B forms a heterodimer with KIF3A (kinesin-like protein KIF3A); (KIF3A/3B), that is membrane-bound and has ATPase activity. Then KIFAP3 (KAP3, kinesin superfamily associated protein–3) binds to the tail domain to form a heterotrimeric motor.[7] This motor has a plus end-directed microtubule sliding activity that exhibits a velocity of ~0.3 μm/s a.[8] There are 14 kinesin protein families in the kinesin superfamily and KIF3B is part of the Kinesin-2 family, of kinesins that can all form heterotrimeric complexes.[9] Expression of the three motor subunits is ubiquitous. The KIG3A/3B/KAP3 motors can transport 90 to 160 nm in diameter organelles.[7]
There are many orthologous KIF3B genes that are expressed in Drosophila, the sea urchin, Bos taurus, Canis familiaris, Equus caballus, Felis catus, Macaca mulatta, Mus musculus, Pan troglodytes, and Rattus norvegicus.