MOVEMENTS OF TRUNCATED KINESIN FRAGMENTS WITH A SHORT OR AN ARTIFICIAL FLEXIBLE NECK

To investigate the role of the neck domain of kinesin, we used optical trapping nanometry to perform high-resolution measurements of the mov ements and forces produced by recombinant kinesin fragments in which t he neck domains were shortened or replaced by an artificial random coi l. Truncated kinesin fragments (K351) that contain a motor domain cons isting of approximate to 340 aa and a short neck domain consisting of approximate to 11 aa showed fast movement (800 nm/s) and 8-nm steps. S uch behavior was similar to that of recombinant fragments containing t he full-length neck domain (K411) and to that of native kinesin. Kines in fragments lacking the short neck domain (K340), however, showed ver y slow movement (< 50 nm/s), as previously reported. Joining an artifi cial ll-aa sequence that was expected to form a flexible random chain to the motor domain (K340-chain) produced normal fast (approximate to 700 nm/s) and stepwise movement. The results suggest that the neck dom ain does not act as a rigid lever arm to magnify the structural change at the catalytic domain as has been believed for myosin, but it does act as a flexible joint to guarantee the mobility of the motor domain.