title: X-ray structure and microtubule interaction of the motor domain of Neurospora crassa NcKin3, a kinesin with unusual processivity.
abstract: Neurospora crassa kinesin NcKin3 belongs to a unique fungal-specific subgroup of small Kinesin-3-related motor proteins. One of its functions appears to be the transport of mitochondria along microtubules. Here, we present the X-ray structure of a C-terminally truncated monomeric construct of NcKin3 comprising the motor domain and the neck linker, and a 3-D image reconstruction of this motor domain bound to microtubules, by cryoelectron microscopy. The protein contains Mg.ADP bound to the active site, yet the structure resembles an ATP-bound state. By comparison with structures of the Kinesin-3 motor Kif1A in different nucleotide states (Kikkawa, M. et al. (2001) Nature (London, U.K.) 411, 439-445), the NcKin3 structure corresponds to the AMPPCP complex of Kif1A rather than the AMPPNP complex. NcKin3-specific differences in the coordination of the nucleotide and asymmetric interactions between adjacent molecules in the crystal are discussed in the context of the unusual kinetics of the dimeric wild-type motor and the monomeric construct used for crystal structure analysis. The NcKin3 motor decorates microtubules at a stoichiometry of one head per alphabeta-tubulin heterodimer, thereby forming an axial periodicity of 8 nm. In spite of unusual extensions at the N-terminus and within flexible loops L2, L8a, and L12 (corresponding to the K-loop of monomeric kinesins), the microtubule binding geometry is similar to that of other members of the kinesin family.
authors.affiliation: Max-Planck-Unit for Structural Molecular Biology, Notkestrasse 85, 22607 Hamburg, Germany. marx@mpasmb.desy.de
authors.forename: Alexander
authors.initials: A
authors.lastname: Marx
authors.forename: Jens
authors.initials: J
authors.lastname: Müller
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Mandelkow
authors.forename: Günther
authors.initials: G
authors.lastname: Woehlke
authors.forename: Cedric
authors.initials: C
authors.lastname: Bouchet-Marquis
authors.forename: Andreas
authors.initials: A
authors.lastname: Hoenger
authors.forename: Eckhard
authors.initials: E
authors.lastname: Mandelkow
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D005656:Fungal Proteins / Q000737:chemistry*; D008870:Microtubules / Q000737:chemistry*; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000737:chemistry*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D005656:Fungal Proteins; D020409:Molecular Motor Proteins