Unusual properties of the fungal conventional kinesin neck domain from Neurospora crassa

Fungal conventional kinesins are unusually fast microtubule motor proteins. To compare the functional organization of fungal and animal conventional k inesins, a set of C-terminal deletion mutants of the Neurospora crassa conv entional kinesin, NcKin, was investigated for its biochemical and biophysic al properties. While the shortest, monomeric construct comprising the catal ytic core and the neck-linker (NcKin343) displays very high steady-state AT Pase (k(cat) = 260/s), constructs including both the full neck and- adjacen t hinge domains (NcKin400, NcKin433 and NcKin480) show wild-type behaviour: they are dimeric, show fast gliding and slower ATP turnover rates (k(cat) = 60-84/s), and are chemically processive. Unexpectedly, a construct (NcKin 378, corresponding to Drosophila KHC381) that includes just the entire coil ed-coil neck is a monomer. Its ATPase activity is slow (k(cat) = 27/s), and chemical processivity is abolished. Together with a structural analysis of synthetic neck peptides, our data demonstrate that the NcKin neck domain b ehaves differently from that of animal conventional kinesins and may be tun ed to drive fast, processive motility.