CBE Seminar: Shunji Egusa

Assistant Professor, Department of Physics, Center for Biomedical Engineering & Science, The University of North Carolina Charlotte

Mechanism of the Fluorescence in Protein-Gold Complexes

 

Abstract
I will discuss new findings on the red fluorophore in the bovine serum albumin (BSA)-gold (Au) compound, initially described by Xie et al. (J. Am. Chem. Soc. 2009, 131, 888-889) as Au25 nanoclusters. We examined the correlations between BSA conformations (pH-induced as well as denatured) and the resulting fluorescence of BSA-Au complexes. The red fluorescence of the BSA-Au complex was associated with a particular isoform of BSA, the aged form (A-form, pH > 10) of the five pH-dependent reversible BSA conformations, while the other conformations did not yield red fluorescence. We identified multiple specific Au(III) binding sites in BSA. In addition, we found a significant degree of non-specific Au(III) binding on BSA surface. Time-course of the emergence of the red fluorescence was measured in detail. The red fluorophore formation was a slow yet dynamic process, which was consistent with the pH-induced equilibrium transition between the conformations of BSA. Notably, the kinetic rate of the fluorophore formation was not strongly dependent on the concentration of Au(III). We propose a new mechanism of the red fluorophore formation based on Langumuir-type adsorption of Au(III) to BSA, as an alternative to the single-site nucleation model of a neutral Au25 nanocluster.

Bio:
Shunji Egusa received Ph.D. in physics from the University of Chicago. He subsequently completed postdoctoral training in materials science & engineering at MIT, and in cancer biology at Cleveland Clinic. He is a recipient of the new investigator awards from PhRMA Foundation, Leukemia Research Foundation, and NASA-NC Space Grant. NIH and NSF/IUCRC additionally support the research of Egusa lab, toward understanding the mechanisms of nano-materials chemistry, and for the applications of nano-materials. The current projects include nano-medicine to improve cancer (leukemia) chemotherapy, fluorescent protein-metal complexes, nanofluids, and synthesis of phase-changing nano-materials.