Nanoscale Optical Methods for Revealing Molecular Organization in Biological Membranes

Many essential biological processes depend on the interaction of lipids, proteins, and carbohydrates that occur on the 10s of nanometer length scale. However, the diffraction-limit of conventional optical microscopes prevents the resolution of structures smaller than 200 nm. Kelly is developing novel optical methods to elucidate the interdependence of molecular organization, lipid phase, and membrane curvature. With near-field fluorescence cross-correlation spectroscopy, he has resolved the single-molecule cross-linking of membrane proteins in the initial stage of an immunological response. With polarized localization microscopy, he has resolved membrane curvature and molecular reorganization with 20 nm uncertainty. Recently, he has demonstrated that cholera toxin subunit B self assembles to form nanoscale membrane buds to facilitate its immobilization and internalization into cells. Kelly will discuss the physics of these optical methods and what they have revealed about the biophysics of membranes. In sum, he aims to reveal the basic physical mechanisms governing complex biological processes by pushing the limits of optical techniques.