Kinesin-motor Unc104 interacts with membrane cargo via its PH domain

Dieter Klopfenstein and Ron Vale


Kinesin-family member Unc104/KIF1A is conserved from Dictyostelium to humans and is involved in microtubule-dependent vesicle transport. While little is known about the molecular mechanism how this motor interacts with its vesicular cargo, a candidate membrane interaction region is a pleckstrin homology (PH) domain located at the C-terminus of the motor protein. We show here that the PH domain of Dictyostelium Unc104 is sufficient for binding to and transporting protein-free liposomes composed of phophatidylinositol-4,5-bisphosphate (PtdIns-4,5-P2). The PH domain binds to and transports native and trypsinized Dictyostelium vesicles along microtubules in an in vitro assay. This suggests that lipid binding may be important for binding native vesicles although membrane proteins are likely to play a role as well. To further demonstrate that the PH domain is the critical cargo binding domain, we show that a mini-Unc104 consisting of the motor domain fused directly to the minimal PH domain is sufficient to reconstitute Dictyostelium vesicle and liposome transport. Moreover, the PH domain can be substituted for the tail domain of mitotic minus-end directed motor ncd and the chimeric motor will transport vesicles towards the microtubule-minus end. Taken together, our data suggest that the PH domain of Unc104 functions as a cargo binding domain for vesicle transport.

ASCB 2001