Nanomechanics Studies of Biomolecules Using Optical Tweezers

Abstract

Although many proteins in human cells have been identified, the structure-function relationships for most of them remain unknown. For example, protein motors such as kinesin and dynein were identified a long time ago but the exact mechanisms driving the motors are still elusive. Further, many protein molecules exhibit complex conformational dynamics which plays an important regulatory role in their functions. While it was common knowledge that DNA forms a double helix and that the helix is unwound by enzymes for transcription, the forces required to untwist the DNA was uncovered just recently. In carrying out nanomechanics studies of biomolecules such as DNA and proteins, we hope to answer some of the fundamental questions and more generally, to characterize the mechanical behavior of single molecules. The characteristics we wish to define include how a protein molecule deforms, unfolds, responds to a force and generates a force. Most proteins are small (1–100 nm) and the amplitudes of their deformation are even smaller, preventing them from being visible to a light microscope. Atomic force microscopy (AFM) can be used to measure the force-extension curves of proteins but the use of AFM is limited by the relatively high thermal noise. Thus, we elected to build an optical tweezers, a measurement system that can accurately measure forces in the range of 0.5–50 pN.