Analysis of heterodimer formation by Xklp3A/B, a newly cloned kinesin-II from Xenopus laevis

kinesin-II motor proteins are composed of two different kinesin-like motor proteins and one cargo binding subunit, Here we report the cloning of a new member of the kinesin-II superfamily, Xklp3A from Xenopus laevis, which fo rms a heterodimeric complex with Xklp3B, The heterodimer formation properti es between Xklp3A and B have been tested in vitro using reticulocyte lysate expression and immnnoprecipitation, To this end we produced a series of Xk lp3A and B constructs of varying length and tested their propensity for het erodimer formation. We could demonstrate that, in contrast to conventional kinesin, the critical domains for heterodimer formation in Xklp3A/B are loc ated at the C-terminal end of the stalk. Neither the neck nor the highly ch arged stretches after the neck region, which are typical of kinesins-II, ar e required for heterodimer formation, nor do they prevent homodimer formati on. Dimerization is controlled by a cooperative mechanism between the C-ter minal coiled-coil segments. Classical trigger sites were not identified. Th e critical regions for dimerization exhibit a very high degree of sequence conservation among equivalent members of the kinesin-II family.