Optical Imaging Of Ligand-Protein Binding

A new technique called PHOTON (photostable optical nanoscopy) achieves sufficiently fine resolution to enable detailed optical spectroscopic imaging of ligand-binding sites on individual protein molecules (Nanoscale, DOI: 10.1039/c1nr10182j). Such sites can be imaged crystallographically, but this requires that the protein first be crystallized, and crystallography is incapable of following binding kinetics and real-time conformational changes. PHOTON, developed by Tao Huang and Xiao-Hong Nancy Xu of Old Dominion University, uses an optical microscope to analyze scattered light by single-molecule silver nanoparticle optical biosensors. The technique achieves 1.2-nm spatial and 100-millisecond time resolution, compared with 20-nm spatial and minute to hour time resolution previously. Huang and Xu use PHOTON to image single biotin molecules and their binding sites on the protein streptavidin. The technique does not cause fluorescence, decomposition, or toxicity in living cells, making it possible to study living microorganisms for extended periods of time, Xu notes.