Motor enzymes are remarkable molecular machines that catalyze a chemical reaction, capture the free energy released by the reaction, and use this energy to perform biologically useful mechanical work. Two major groups of these enzymes are the cytoskeletal motors (myosins, dyneins, and kinesins) that move on tracks made of the cytoskeletal proteins actin and tubulin, and the nucleic acid motors (polymerases, helicases, and topoisomerases) that move on DNA or RNA molecules. To learn how such enzymes work, we study them in vitro using conventional biochemical methods, together with light microscopy techniques that visualize nanometer-scale movements and individual chemical reaction events in single enzyme molecules. Understanding the mechanism of a motor enzyme requires answering the questions: "How does the enzyme move along its track?", "How are the chemical processes catalyzed by the enzyme coupled to movement?", and "How is enzyme movement regulated so as to accomplish a biologically useful task?" I will describe experiments that address these questions taken from our studies of E. coli RNA polymerase, a nucleic acid motor, and kinesin, a cytoskeletal motor.
References:
Yin, H., Wang, M. D., Svoboda, K., Landick, R., Block, S. M., & Gelles, J. (1995) Science 270, 1653-1657.
Finzi, L., & Gelles, J. (1995) Science 267, 378-380.
Schafer, D. A., Gelles, J., Sheetz, M. P., & Landick, R. (1991) Nature 352, 444-448.