Part of a kinesin motor-adapter complex that is critical for the anterograde axonal transport of active zone components and contributes to activity-dependent presynaptic assembly during neuronal development. Interacts with STX1A and KIF5B. Colocalizes with syntaxin vesicles along microtubules in neuronal processes. Isoform 3, isoform 4 and isoform 5 are expressed in HeLa cell line (at protein level). Isoform 3 is expressed in fetal and adult brain. Isoform 4 is expressed in numerous fetal tissues (brain, kidney, liver, lung, and thymus) and in adult brain, kidney, liver, lung, pancreas, colon, prostate, small intestine, testis and thymus. Isoform 5 is expressed in fetal brain, brain and small intestine.