Steven Block, S. W. Ascherman Professor of the Sciences, Stanford University
Technical advances have led to the new field of single molecule biophysics. Singlemolecule methods can record characteristics that are obscured by traditional, ensemblebased biochemical approaches, revealing rich behaviors in individual biomolecules. An entire arsenal of techniques with singlemolecule sensitivity has now been developed. Prominent among the technologies is the laser optical trap, or "optical tweezers," which is based upon radiation pressure. Optical trapping microscopes now routinely measure biomolecular properties with precision down the atomic level—currently achieving a resolution of ~1 angstrom over a bandwidth of ~100 Hz—all while exerting exquisitely controlled forces in the piconewton (pN) range. Among the notable successes for optical traps have been measurements of the fundamental steps produced by motor proteins (for example, kinesin and myosin) and by processive nucleic acid enzymes (for example, RNA polymerase), as well as measurements of the strengths of noncovalent bonds between proteins, and the kinetics of structure formation in polymers such as DNA and RNA. Optical trapping instruments have been particularly useful in mapping out the energy landscapes for folding macromolecules. These instruments have even been able to follow the cotranscriptional folding of RNA in real time, as it's synthesized by RNA polymerase, revealing how such folding can regulate downstream genes, mediated by a class of structured RNAs known as "riboswitches." In recent developments, optical traps are being used in combination with single-molecule FRET (Förster Resonance Energy Transfer) to report simultaneously on folding configurations and internal degrees of freedom in biomolecules.