Origins of reversed directionality in the ncd molecular motor

• Published in: The EMBO journal Vol. 13; no. 4; pp. 751 - 757
• Main Authors: Lockhart, A., Cross, R.A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 15-02-1994
• Subjects: Adenosine Diphosphate - metabolism; Adenosine Triphosphatases - metabolism; Biological and medical sciences; Cells, Cultured; Diptera; Drosophila; Drosophila Proteins; Drosophilidae; Fundamental and applied biological sciences. Psychology; Glutathione Transferase - genetics; Glutathione Transferase - metabolism; In solution. Condensed state. Thin layers; Kinesins - metabolism; Kinetics; Microtubule Proteins - genetics; Microtubule Proteins - metabolism; Microtubules - metabolism; Molecular biophysics; Nucleotides - metabolism; Physico-chemical properties of biomolecules; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Molecular motion; Enzyme; Escherichia coli; Adenosinetriphosphatase; Mechanism; Enzymatic activity; Turnover; Bacteria; Hydrolases; Microtubule associated protein; Recombinant protein; Direction reversal; ATP; Physicochemical properties; Kinesin; Enterobacteriaceae
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1002/j.1460-2075.1994.tb06317.x

The head or motor domain of the ncd (non‐claret disjunctional) molecular motor is 41% identical to that of kinesin, yet moves along microtubules in the opposite direction to kinesin. We show here that despite the reversed directionality of ncd, its kinetics in solution are homologous in key respects to those of kinesin. The rate limiting step, ADP release, occurs at 0.0033 s‐1 at 100 mM NaCl and is accelerated approximately 1000‐fold when the motor binds to microtubules. Other reaction steps are all very fast (> 0.1 s‐1) compared with ADP release, and the motor is consequently paused in the ncd.ADP state until microtubule binding occurs (Kd = 2 microM), at which point ADP release is triggered and the motor locks onto the microtubule in a rigor‐like state. These data identify close functional homology between the strong binding states of kinesin and ncd, and in view of this we discuss a possible mechanism for directional reversal, in which the strong binding states of ncd and kinesin are functionally identical, but the weak binding states are biased in opposite directions.