THE SHAPES OF THE MOTOR DOMAINS OF 2 OPPOSITELY DIRECTED MICROTUBULE MOTORS, NOD AND KINESIN - A NEUTRON-SCATTERING STUDY

The shapes of the motor domains of kinesin and nod, which move in oppo site directions along microtubules, have been investigated. Using prot eins expressed in Escherichia coli, it was found that at high salt (>2 00 mM) Drosophila nod motor domain (R335-K700) and human kinesin motor domain (M1-E349) were both sufficiently monomeric to allow an accurat e determination of their radii of gyration (R(g)) and their molecular weights. The measured R(g) values of the ncd and kinesin motor domains in D2O were 2.06 +/- 0.06 and 2.05 +/- 0.04 nm, respectively, and the molecular weights were consistent with those computed from the amino acid compositions. Fitting of the scattering curves to similar to 3.5 nm resolution showed that the ncd and kinesin motor domains can be des cribed adequately by triaxial ellipsoids having half-axes of 1.42 +/- 0.38, 2.24 +/- 0.44, and 3.65 +/- 0.22 nm, and half-axes of 1.52 +/- 0 .23, 2.00 +/- 0.25, and 3.73 +/- 0.10 nm, respectively. Both motor dom ains are described adequately as somewhat flattened prolate ellipsoids with a maximum dimension of similar to 7.5 nm. Thus, it appears that the overall shapes of these motor domains are not the major determinan ts of the directionality of their movement along microtubules.