Biochemistry

Synchronized Stepping

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Science  07 Oct 2011:
Vol. 334, Issue 6052, pp. 17
DOI: 10.1126/science.334.6052.17-c

Inside the cell, ensembles of different myosin proteins attached to a single cargo molecule allow for bidirectional transport along actin tracks. To gain insight into the coordination that must be required to deliver the cargo to its destination, Ali et al. labeled myosin V (myoV) and myosin VI (myoVI), which move in opposite directions, with different colored quantum dots. They coupled the motors through a third quantum dot cargo and used total internal fluorescence microscopy to determine the stepping dynamics of each individual motor. Though the motors have similar stall forces, myoV dominated ∼80% of the time, probably because it has a higher unbinding force than myoVI. Regardless of which motor won, its movement was significantly slowed by the losing motor which, interestingly, took continuous backward steps coincident with the forward steps of the winning motor. In the presence of micromolar concentrations of ADP, myoVI dominated by acting as an anchor that prevented myoV from stepping forward. The dominant motor could also be shifted by varying the myoV:myoVI:cargo conjugation ratio, consistent with regulation by varying the ratio of motor types bound to cargo. Such approaches that provide a mechanochemical understanding of motor coupling will be valuable in efforts to model the regulatory mechanisms that govern intracellular transport.

Proc. Natl. Acad. Sci. U.S.A. 108, E535 (2011).

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