Structural characterization of a minimal KLC2/Nup358/BicD2 complex

Abstract

Cellular transport processes along microtubules are often facilitated by multi-motor complexes, which are connected by adapter proteins and cargoes. The nuclear pore protein Nup358, for example, interacts with the dynein adapter Bicaudal D2 (BicD2), which in turn recruits minus-end directed dynein motors and plus-end directed kinesin-1 motors for a nuclear positioning pathway that is essential for brain development. How motor recruitment is regulated by interactions of BicD2 with Nup358 is not well understood. Here, we characterize the structure of a minimal complex of kinesin-1 light chain 2 (KLC2), Nup358 and BicD2 by cryo-electron microscopy and small angle X-ray scattering. KLC2/Nup358 assumes a rod-like structure that increases in thickness, when BicD2 is bound. The addition of BicD2 also shifts the KLC2/Nup358/BicD2 complex towards a 2:2:2 stoichiometry, promoting dimerization at lower protein concentrations than without BicD2. Similarly, the presence of the Nup358/KLC2 interaction results in a shift towards a 2:2:2 stoichiometry. Based on these results, we hypothesize that KLC2 and BicD2 are recruited to Nup358 in a cooperative manner, and cooperativity may be promoted by modulation of the oligomeric state.