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

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Abstract
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 forms a heterodimeric complex with Xklp3B. The heterodimer formation properties between Xklp3A and B have been tested in vitro using reticulocyte lysate expression and immunoprecipitation. To this end we produced a series of Xklp3A and B constructs of varying length and tested their propensity for heterodimer formation. We could demonstrate that, in contrast to conventional kinesin, the critical domains for heterodimer formation in Xklp3A/B are located at the C‐terminal end of the stalk. Neither the neck nor the highly charged stretches after the neck region, which are typical of kinesins‐II, are required for heterodimer formation, nor do they prevent homodimer formation. Dimerization is controlled by a cooperative mechanism between the C‐terminal coiled‐coil segments. Classical trigger sites were not identified. The critical regions for dimerization exhibit a very high degree of sequence conservation among equivalent members of the kinesin‐II family.

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