Yale E. Goldman, MD, PhD, University of Pennsylvania

Structural Dynamics by Single Molecule Biophysical Approaches: Polarized Fluorescence Microscopy and High-Speed Laser Tweezers

Molecular motors are ‘smart’ protein nanomachines that enable muscle and heart contraction and carry essential intracellular cargos to specific destinations within each cell. Myosin is the molecular motor that travels along intracellular actin cytoskeletal filaments to perform these tasks. A relatively new approach to studying cell biological systems, termed single molecule biophysics, makes use of novel instrumentation and quantitative analysis to obtain details not available from classical biochemical methods on millions of molecules. Taking an average always loses information about the true distribution among individuals! Our single molecule experiments on the myosin V motor showed how it walks along actin filaments “hand-over-hand” to avoid “losing track”. It can’t derive energy from its chaotic environment, but nevertheless, it harnesses local fluctuations usefully. The linkage between elementary steps in the enzymatic cycle of myosin motors and transduction of chemical energy into mechanical work has been controversial for many years. Novel methods using the infrared laser trap, also called laser tweezers, improve temporal resolution some 50-fold, finally showing the sequence of biochemical and mechanical reaction steps. Technology to achieve these improvements, quantitative analysis of the noisy traces, and the conclusions about the mechanism will be explained.