CRYSTAL-STRUCTURE OF THE MOTOR DOMAIN OF THE KINESIN-RELATED MOTOR NCD

MICROTUBULE-BASED ATPases of the kinesin superfamily(1,2) provide the motile force for many animated features of living cells. Kinesin motor s differ in their direction of movement along microtubules. Kinesin(3) and ncd(4,5), a kinesin-related motor involved in formation and maint enance of mitotic and meiotic spindles, move in opposite directions al ong microtubules, even though their motor domains are 40% identical in amino-acid sequence. Here we report the crystal structure of the MgAD P complex of the Drosophila ncd motor domain determined to 2.5 Angstro m by X-ray crystallography, and compare it to the kinesin structure. T he ncd and kinesin motor domains are remarkably similar in structure, and the locations of conserved surface amino acids suggest these motor s share a common microtubule-binding site, Moreover, structural and fu nctional comparisons of ncd, kinesin, myosin and G proteins indicate t hat these NTPases may have a similar strategy of changing conformation between NTP and NDP states. We propose a general model for converting a common gamma-phosphate-sensing mechanism into opposite polarities o f movement for kinesin and ncd.