Role of the kinesin neck linker and catalytic core in microtubule-based motility

Kinesin motor proteins execute a variety of intracellular microtubule-based transport functions [1], Kinesin motor domains contain a catalytic core, w hich is conserved throughout the kinesin superfamily, followed by a neck re gion, which is conserved within subfamilies and has been implicated in cont rolling the direction of motion along a microtubule [2,3], Here, we have us ed mutational analysis to determine the functions of the catalytic core and the similar to 15 amino acid 'neck linker' (a sequence contained within th e neck region) of human conventional kinesin, Replacement of the neck linke r with a designed random coil resulted in a 200-500-fold decrease in microt ubule velocity, although basal and microtubule-stimulated ATPase rates were within threefold of wildtype levels. The catalytic core of kinesin, withou t any additional kinesin sequence, displayed microtubule-stimulated ATPase activity, nucleotide-dependent microtubule binding, and very slow plus end- directed motor activity. On the basis of these results, we propose that the catalytic core is sufficient for allosteric regulation of microtubule bind ing and ATPase activity and that the kinesin neck linker functions as a mec hanical amplifier for motion, Given that the neck linker undergoes a nucleo tide-dependent conformational change [4], this region might act in an analo gous fashion to the myosin converter, which amplifies small conformational changes in the myosin catalytic core [5,6].