X-RAY CRYSTAL-STRUCTURE OF THE YEAST KAR3 MOTOR DOMAIN COMPLEXED WITHMG-CENTER-DOT-ADP TO 2.3 ANGSTROM RESOLUTION

The kinesin family of motor proteins, which contain a conserved motor domain of similar to 350 amino acids, generate movement against microt ubules. Over 90 members of this family have been identified, including motors that move toward the minus or plus end of microtubules. The Ka r3 protein from Saccharomyces cerevisiae is a minus end-directed kines in family member that is involved in both nuclear fusion, or karyogamy , and mitosis. The Kar3 protein is 729 residues in length with the mot or domain located in the C-terminal 347 residues. Recently, the three- dimensional structures of two kinesin family members have been reporte d. These structures include the motor domains of the plus end-directed kinesin heavy chain [Kull, F. J., et al. (1996) Nature 380, 550-555] and the minus end-directed Ncd [Sablin, E, P., et al. (1996) Nature 38 0, 555-559]. We now report the structure of the Kar3 protein complexed with Mg ADP obtained from crystallographic data to 2.3 Angstrom. The structure is similar to those of the earlier kinesin family members, b ut shows differences as well, most notably in the length of helix alph a 4, a helix which is believed to be involved in conformational change s during the hydrolysis cycle.