IMPORTANCE OF A FLEXIBLE HINGE NEAR THE MOTOR DOMAIN IN KINESIN-DRIVEN MOTILITY

Conventional kinesin is a molecular motor consisting of an N-terminal catalytic motor domain, an extended stalk and a small globular C-termi nus. Whereas the structure and Function of the catalytic motor domain has been investigated, little is known about the function of domains o utside the globular head. A short coiled-coil region adjacent to the m otor domain, termed the neck, is known to be important for dimerizatio n and may be required for kinesin processivity, We now provide evidenc e that a helix-disrupting hinge region (hinge 1) that separates the ne ck from the first extended coiled-coil of the stalk plays an essential role in basic motor activity. A fast fungal kinesin from Syncephalast rum racemosum was used for these studies. Deletion, substitution by a coiled-coil and truncation of the hinge 1 region all reduce motor spee d and uncouple ATP turnover from gliding velocity. Insertion of hinge 1 regions from two conventional kinesins, Nkin and DmKHC, fully restor es motor activity, whereas insertion of putative flexible linkers of o ther proteins does not, suggesting that hinge 1 regions of conventiona l kinesins fan functionally replace each other, We suggest that this r egion is essential for kinesin movement in its promotion of chemo-mech anical coupling of the two heads and therefore the functional motor do main should be redefined to include not only the catalytic head but al so the adjacent neck and hinge 1 domains.