STRUCTURAL CHARACTERIZATION OF A DYNEIN MOTOR DOMAIN

Cytoplasmic dynein is a microtubule-based mechanochemical protein that plays an essential role in cell division, vesicle transport, and cyto plasmic membrane organization. As a molecular motor, dynein utilizes a n ATP hydrolysis mechanism to bind and release microtubules and to und ergo conformational changes that result in a net displacement towards the microtubule's minus end. To visualize structural features of this motor protein, we have begun to characterize the dynein head domain by electron microscopy and image processing. Transmission electron micro scopy of negatively stained native dynein from Dictyostelium has been performed and images of the head domain have been aligned and analyzed with the software SPIDER. The resulting 2D averages show an oblong ro und shape composed of seven to eight globular domains or lobes that en circle a stain-filled area. A recombinant 380 kDa fragment of the dyne in heavy chain encodes just the globular head domain; analysis of thes e particles reveals a high structural similarity with the native head domain. A prominent stalk can be seen in several projections of this f ragment, suggesting a structure analogous to the B-link described for some axonemal dyneins. Single tilt pair images were used to compute lo w resolution 3D reconstructions of the dynein head domain. These show a flattened spheroidal shape of 13.5 nm in length with seven similar d omains arranged in a ring. Slices through the reconstructions reveal a large central cavity. This is the first detailed description of the h ead domain structure for a dynein molecule. The presence of a central cavity and the outer globular features, along with its large size make dynein structurally distinct from either myosin or kinesin. (C) 1998 Academic Press Limited.