In the crucial, repeating step described in the Nature report, the thrusting movement of the lead motor's neck pulls the rear motor free of the track, flinging it on ahead to become the new leader of this two-engine train. Two kinesin motors work as a coordinated team to pull their cargo, one motor just ahead of the other on the tracks. Using four different techniques to visualize and measure changes in the motor's shape, the researchers showed that a small region of the protein called the "neck linker" thrusts forward when powered by ATP, the chemical that serves as a nearly universal energy source inside cells. Research along these lines is already under way in private biomedical labs. Inhibition of kinesins involved in cell division, for example, might provide a means of stopping the growth of cancer cells, and stimulation of kinesin motors involved in nerve transport may improve neurodegenerative diseases. There are likely to be 50 or more different kinds of kinesin motors in humans, their discoverer estimates, and that degree of specificity suggests that the motors might make good drug targets. The mechanism appears to be fundamental to all cells of higher organisms, but with slight modifications engineered to produce different types of motion. Altogether, 15 researchers took part in the project, including Ronald Milligan, PhD, professor of cell biology at Scripps Research Institute who led the effort to obtain images of a key component of the microscopic motor. First author is Sarah Rice, a graduate student in Vale's lab. Senior author is Ronald Vale, PhD, an investigator in the Howard Hughes Medical Institute and professor of cellular and molecular pharmacology at UCSF.
The scientists report their discoveries in the December 16 issue of the journal Nature. While scientists have known for 15 years that kinesin motors pull their cargo by moving along the cells' internal trackways known as microtubules, the new research reveals how the tiny motors, each only about one ten-millionth of an inch across, generate the force to haul objects up to a thousand times their own size. Led by the UC San Francisco scientist who discovered this protein motor called kinesin in 1985, the researchers have now scrutinized and measured how the motor changes shape, and they have deduced the crucial mechanism behind a leapfrog motion that allows the motors to transport material throughout cells.
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