Research Interests
Biological
Electron Transfer, Membrane Biophysics, Vibrational Spectroscopy, EPR
Spectroscopy, Photosynthesis. Oxido-reductase enzymes play central
roles in cellular metabolism. For example, membrane-associated redox enzymes
carry out photosynthetic and respiratory energy conversion. Work in my
laboratory is centered on these enzymes, in particular, on the mechanism
of energy conversion in plant photosynthesis. In plant photosynthesis,
light absorption leads to a long distance electron transfer reaction.
We are interested in how proteins control the direction and rate of the
electron transfer reactions and in how the electron transfer reactions
are coupled with protonation reactions, conformational changes, and other
chemical reactions, such as photosynthetic oxygen production. We study
the structure and function of photosynthetic reaction centers that have
been isolated from plants and cyanobacteria. We are also building simple
models of these complex proteins, in order to elucidate fundamental principles.
To reach our goals, my laboratory employs a broad combination of techniques,
including vibrational spectroscopy, EPR spectroscopy, site-directed mutagenesis,
and mass spectrometry.
Post-translational modifications in membrane proteins. Amino acid side chains in proteins can be modified during or after the synthesis of the protein. The modified amino acid may have unique reactivity or may provide a cellular signal. There is little known about such modifications in photosynthetic enzymes. My group is using mass spectrometry and peptide mapping to identify interesting, modified amino acids in a photosynthetic membrane protein, photosystem II. A subset of these modified amino acids are located at the active site for water oxidation and may play a role in the structure and function of the enzyme. Other photosystem II modifications may be important in signaling for the turnover or degradation of the enzyme inside the cell.
Electron transfer in enzymes and in model compounds. Long distance electron transfer in proteins involves step-wise reactions between pairs of redox-active prosthetic groups, which act as catalytic intermediates. These prosthetic groups include covalently and non-covalently bound cofactors, such as heme, pheophytin, and chl, as well as amino acid side chains. An important long-term goal of this research project is to determine how electron transfer rates are influenced by changes in the structure and environment of these redox intermediates. We are investigating electron transfer mechanisms that involve redox-active amino acids in enzymes and in model peptides. We are using EPR and time-resolved vibrational spectroscopy, and, in collaborative efforts, electron spin-echo envelope modulation (ESEEM) and density functional (DFT) calculations. We are also investigating electron transfer mechanisms that involve tetrapyrrole-derived cofactors. This work will help to elucidate the factors responsible for midpoint potential control in oxido-reductases.
S. Kim and B. A. Barry. "Reaction-induced FT-IR spectroscopic studies of biological energy conversion in photosynthesis and transport." (2001) Journal of Physical Chemistry B (Feature Article-Cover Art) 105, 4072-4083.
Oxygen production in plant photosynthesis. Oxygenic photosynthesis is essential in the maintenance of life on earth. This type of photosynthesis requires the concerted action of two reaction centers, which convert light energy into a transmembrane charge separation. One of these reaction centers, photosystem II (PSII) catalyzes the oxidation of water and the production of molecular oxygen. PSII accumulates the four oxidizing equivalents necessary for oxygen production at a manganese-containing catalytic site. PSII consists both of integral, membrane-spanning subunits and of extrinsic subunits, that do not span the membrane. The extrinsic subunit known as the manganese stabilizing protein, MSP, prevents loss of manganese from the PSII active site and is required for optimal rates of oxygen evolution. In this project, vibrational spectroscopy is being used to obtain detailed information about structural changes occurring during oxygen production. The ultimate goal is to determine how oxygen-oxygen bond formation occurs. In addition, vibrational spectroscopy is being employed to test a possible mechanism by which MSP may influence water oxidation. Finally, in a collaborative small angle X-ray scattering project, the hypothesis that MSP changes conformation when it binds to PSII is being tested. These experiments will provide new information about the function and assembly of complex membrane proteins.
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Last Update: May 30, 2007
