title: Fast or Slow, Either Head Can Start the Processive Run of Kinesin-2 KIF3AC.
abstract: Mammalian KIF3AC contains two distinct motor polypeptides and is best known for its role in organelle transport in neurons. Our recent studies showed that KIF3AC is as processive as conventional kinesin-1, suggesting that their ATPase mechanochemistry may be similar. However, the presence of two different motor polypeptides in KIF3AC implies that there must be a cellular advantage for the KIF3AC heterodimer. The hypothesis tested was whether there is an intrinsic bias within KIF3AC such that either KIF3A or KIF3C initiates the processive run. To pursue these experiments, a mechanistic approach was used to compare the pre-steady-state kinetics of KIF3AC to the kinetics of homodimeric KIF3AA and KIF3CC. The results indicate that microtubule collision at 11.4 μM(-1) s(-1) coupled with ADP release at 78 s(-1) are fast steps for homodimeric KIF3AA. In contrast, KIF3CC exhibits much slower microtubule association at 2.1 μM(-1) s(-1) and ADP release at 8 s(-1). For KIF3AC, microtubule association at 6.6 μM(-1) s(-1) and ADP release at 51 s(-1) are intermediate between the constants for KIF3AA and KIF3CC. These results indicate that either KIF3A or KIF3C can initiate the processive run. Surprisingly, the kinetics of the initial event of microtubule collision followed by ADP release for KIF3AC is not equivalent to 1:1 mixtures of KIF3AA plus KIF3CC homodimers at the same motor concentration. These results reveal that the intermolecular communication within the KIF3AC heterodimer modulates entry into the processive run regardless of whether the run is initiated by the KIF3A or KIF3C motor domain.
authors.affiliation: From the Department of Biological Sciences and the Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180 and.
authors.forename: Pengwei
authors.initials: P
authors.lastname: Zhang
authors.affiliation: the Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706.
authors.forename: Ivan
authors.initials: I
authors.lastname: Rayment
authors.affiliation: From the Department of Biological Sciences and the Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180 and sgilbert@rpi.edu.
authors.forename: Susan P
authors.initials: SP
authors.lastname: Gilbert
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000465:Algorithms; D000818:Animals; D055162:Biocatalysis; D020134:Catalytic Domain; D019281:Dimerization; D016547:Kinesins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008870:Microtubules / Q000378:metabolism; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D062367:ortho-Aminobenzoates / Q000378:metabolism
chemical_list: C490202:Kif3a protein, mouse; C484676:Kif3c protein, mouse; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D062367:ortho-Aminobenzoates; D000244:Adenosine Diphosphate; C045473:3'-O-(N-methylanthraniloyl) ATP; D000255:Adenosine Triphosphate; D016547:Kinesins
keywords: ATPase; intracellular trafficking; microtubule; neuron; pre-steady-state kinetics; processivity