Interdomain interactions in the KIF3 kinesin family motor

Kinesins comprise a family of molecular motors that transport intracellular cargo along microtubules. While the performance of conventional kinesin has received considerable attention, much less is known about the design features and performance of other kinesins. KIF3A/B is an especially intriguing kinesin because it contains two non-identical heads, a design that may confer added speed, affinity, strength, or some other ability. To test KIF3A/B function, we have expressed and purified full-length motors in a eukaryotic expression system and investigated their motility and biochemistry using in vitro assays. KIF3A/B moves microtubules at approximately 20% the speed of conventional kinesin. Individual KIF3A/B motors are able to support motility in the microtubule gliding assay, though the microtubule affinity is less than conventional kinesin. Hence, the design advantage of having two different motor domains appears to be neither the speed of movement nor the affinity for microtubules.