Bioinorganic and Biophysical Chemistry
Our studies examine the interplay between protein dynamics and redox reactivity in signaling transformations. We focus primarily on bioinorganic systems where intrinsic or engineered metal sites provide access to unique chemistry and rich spectroscopy. We employ a wide range of experimental approaches including development and synthesis of new protein dynamics probes, mutational analysis in vitro and in vivo, and time-resolved optical spectroscopy. Powerful measurements of electron- and energy-transfer kinetics allow us to observe and quantitatively characterize conformational transitions, determine structural changes and corresponding energy barriers, as well as evaluate composition of heterogeneous ensembles. As these experiments map the entire energy landscapes of protein folding and function, they provide a detailed framework for understanding signaling transformations and redox reactivity.
Release of the heme protein cytochrome c (cyt c) from mitochondria is a critical signaling step in execution of apoptosis. Upon binding to mitochondrial membranes, cyt c acquires peroxidase activity, which is important for its apoptotic release. With time-resolved fluorescence and phosphorescence techniques, we are investigating conformational properties of the cardiolipin-bound cyt c and correlate them to the protein peroxidase activity. In collaboration with Barbara Conradt's group we are also developing methods for monitoring conformational state of cyt c during C. elegans apoptosis in vivo. These studies are yielding structural information about apoptotic cyt c and the mechanism of its release, which are important for the design of apoptotic regulators.
Redox-linked Ligand Substitution
We are studying a group of proteins, in which changes in the oxidation state of the heme are linked to heme ligand substitution resulting in protein conformational rearrangements. Current work is focused on cyt c mutants and several heme sensors. We are investigating their redox reactivity, ligand substitution and folding. Kinetics of photoinduced redox reactions form the cornerstone of this research. These studies not only explore important problems in coordination chemistry and redox mechanisms but could also provide valuable insights for design of molecular systems with switchable redox properties for solar-energy harvesting.
Our collaborative efforts include mechanistic studies of functional refolding (with Peter Wolynes at UCSD) and analysis of effects of arsenic on actin structure and functional dynamics (with Henry Higgs and Scott Gerber at Dartmouth Medical School).