Recombinant kinesin motor domain binds to β-tubulin and decorates microtubules with a B surface lattice

We have expressed the recombinant squid kinesin head domain in Escherichia coli and studied its interaction with microtubules. The head is active as a microtubule-stimulated ATPase and binds to microtubules, but it does not support microtubule gliding by itself. The head binds to both microtubules and depolymerized tubulin. In each case the zero-length crosslinker 1-ethyl-3-[3-(dimethylamino)propyl] carbodiimide induces a bond specifically to β- but not α-tubulin. The head decorates brain microtubules with an 8-nm axial spacing. Thus the stoichiometrv is one kinesin head per tubulin dimer. The lattice is that of flagellar B-tubules, implying that reassembled microtubules are not symmetric. Moreover, the A- and B-tubules of intact flagellar outer doublets are both decorated with a B lattice. This suggests that the B lattice is a general property of microtubules.