THE COILED-COIL HELIX IN THE NECK OF KINESIN

Kinesin is a microtubule-dependent motor protein. We have recently det ermined the X-ray structure of monomeric and dimeric kinesin from rat brain. The dimer consists of two motor domains, held together by their cy-helical neck domains forming a coiled coil. Here we analyze the na ture of the interactions in the neck domain (residues 339-370). Overal l, the neck helix shows a heptad repeat (abcdefg)(n) typical of coiled coils, with mostly nonpolar residues in positions a and d. However, t he first segment (339-355) contains several nonclassical residues in t he a and d positions which tend to weaken the hydrophobic interaction along the common interface. Instead, stabilization is achieved by a hy drophobic ''coat'' formed by the a and d residues and the long aliphat ic moieties of lysines and glutamates, extending away from the coiled- coil core. By contrast, the second segment of the kinesin neck (356-37 0) shows a classical leucine zipper pattern in which most of the hydro phobic residues are buried at the highly symmetrical dimer interface. The end of the neck reveals the structure of a potential coiled-coil ' 'trigger'' sequence, (C) 1998 Academic Press.