The School of Molecular and Cellular Biology at the University of Illinois at Urbana-Champaign

Research in my lab addresses the basic question of how protein structure determines function, especially in the context of membrane proteins that catalyze electron and proton transfer in biological energy conversion. Our approach is physical biochemistry, using kinetic and spectroscopic methods combined with site directed mutagenesis. The fundamental question may be broken down to several more specific questions, with very general significance for mechanistic biology:

1. how do proteins recognize and bind other molecules (antigens, substrates, cofactors, inhibitors, and other proteins) with great specificity?
2. how are cofactor properties modified through protein-ligand interactions?
3. how are protons transferred through proteins (the vast majority of biological catalytic mechanisms involve proton transfers)?
4. how are electrons transferred from one redox center to another, over long distances?
5. what is the role of conformational mobility in protein function?

Our primary research materials are membrane proteins and membrane preparations of bacterial and plant photosynthesis, and respiration, especially the reaction centers and cytochrome bc1 complexes of purple bacteria. These, and other, multifunctional membrane protein complexes transform energy input (light and food) into metabolic electrochemical free energy with high efficiency and yield. Conversion occurs in reaction sequences that span picoseconds to seconds and involving very many cofactors, e.g., hemes, chlorophylls, iron sulfur centers, quinones, flavins. The structures of many of these large complexes have been determined by X-ray diffraction to about 2 Å resolution, a level of structural detail that allows us to seek mechanistic understanding at a molecular level. The extreme functionality of these proteins - the reaction center has at least 8 distinct forward and backward electron transfer steps - makes these studies both challenging and rich in prospects. As well as providing the sites of chemical reaction, the many cofactors exhibit a wealth of spectroscopic characteristics, making them unparalleled in the observability of their functions and the underlying interactions that determine them.

Working with isolated protein complexes and with intact membranes, we are using biochemical and biophysical techniques (e.g., UV-vis kinetic spectroscopy, FTIR (Fourier transform infrared) spectroscopy, EPR, X-ray crystallography, photovoltage measurement, electrochemistry), mutagenesis, and computational methods to study: (1) charge separating and stabilizing reactions - intra-protein electron and proton transfer; (2) electrogenic steps in biological energy conversion - trans-membrane electron and proton transfer; (3) cofactor binding and modulation of function by the protein; and (4) protein electrostatics and conformational dynamics.

The reaction center from the photosynthetic bacterium Rhodobacter sphaeroides (the membrane plane is horizontal). The quasi-two fold symmetry axis, which runs vertically, creates pairs of identical cofactors with very different properties. Examination of the protein-cofactor interactions provides insight to how Nature works at the atomic level..