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

Our work is based on the complementarities between biophysical, structural and molecular engineering approaches to the study of biological mechanism. The utility of molecular engineering for modification of protein structure is greatly increased by combining this with other approaches. Most importantly, knowledge of the structure of the target protein from crystallography and spectroscopy and the ability to assay the functional consequences of specific mutagenesis make it possible to explore the mechanism of catalysis at the molecular level.

Ubiquinol:cytochrome c2 oxidoreductase (bc1 complex) of Rb. sphaeroides. With crystallographic structures now available, we are able to take advantage of spectroscopic techniques and protocols for protein engineering that allow us to modify the three catalytic subunits, and ask specific questions about the structure, function and topology of the complex. Our studies have revealed novel mechanisms of electron transfer in the bc1 complex; one involves a dramatic domain movement of the extrinsic domain of the iron sulfur protein; more tentative is another proposal for movement of a semiquinone intermediate at the catalytic site. Detailed spectroscopic studies (ESEEM, ENDOR, resonance Raman) allow us to probe structure local to catalytic intermediates that are not accessible through crystallography. We are currently studying these using a variety of biophysical, biochemical and molecular engineering approaches, including several local and international collaborative projects.

In photosystem II, our present work centers on the function and structure of the two-electron gate through which the photosystem reduces the plastoquinone pool, and on the mechanism of oxygen evolution. Structures now available confirm the conformation we predicted for the QB-site of photosystem II, and therefore lend support to the conclusions drawn from biophysical assays for the reactions, and mutagenesis using PCR-based in Chlamydomonas.

Other interests include biophysical aspects of electron transfer and the coupling to ATP synthesis through the proton gradient; studies of the control of photosynthetic electron transfer in the coupled steady-state; the supramolecular organization of electron transfer chains; the mechanism and evolution of the cyt bc1/b6f family of complexes in plants and bacteria; and the mechanism of action of inhibitors (including herbicides). We have developed novel instruments that allow us to explore individual reactions of the photosynthetic apparatus in intact plants. We are using these in the lab and in the field to try to understand how photosynthesis is regulated under natural conditions, including studies of the mechanisms of down regulation in strong light, photo-inhibition, and response to environmental stress, including insect herbivory. Attempts to quantify global energy fluxes in the biosphere introduce questions about the role of information content, leading to more philosophical interests.