3-DIMENSIONAL STRUCTURE OF THE KINESIN HEAD-MICROTUBULE COMPLEX

KINESIN is a microtubule (MT)-associated 'motor' molecule fundamental to organelle transport(1,2). Recently, various kinesin superfamily mem bers (KIFs) have also been identified and suggested as being responsib le for the transport of specific organelles(3-5). Kinesin is a heterot etramer composed of two heavy chains and two light chains. The heavy c hains form two globular heads, a rod and a fan-like tail completed by the light chains(6,7). The globular head, which is composed of approxi mately 340 amino-terminal residues of the heavy chain, includes both A TP-binding and MT-binding domains, and its recombinant protein also ha s these properties(8). To improve the understanding of the mechanism o f force generation by an MT-based molecular motor, kinesin, we report here the three-dimensional structure of the complex of a recombinant k inesin head and MTs, as revealed by helical reconstruction from cryoel ectron micrographs. A kinesin head is a globular teardrop-like structu re binding to the ridge of one protofilament of MTs. We have determine d the polarity of the structure of the complex of MTs and the kinesin head in relation to MT polarity.