FTIR difference spectroscopy of bacteriorhodopsin: Toward a molecular model |
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Authors: | Kenneth J. Rothschild |
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Affiliation: | (1) Departments of Physics and Physiology and the Program in Cellular Biophysics, Boston University, 590 Commonwealth Avenue, 02215 Boston, Massachusetts |
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Abstract: | Bacteriorhodopsin (bR) is a light-driven proton pump whose function includes two key membrane-based processes, active transport and energy transduction. Despite extensive research on bR and other membrane proteins, these processes are not fully understood on the molecular level. In the past ten years, the introduction of Fourier transform infrared (FTIR) difference spectroscopy along with related techniques including time-resolved FTIR difference spectroscopy, polarized FTIR, and attenuated total reflection FTIR has provided a new approach for studying these processes. A key step has been the utilization of site-directed mutagenesis to assign bands in the FTIR difference spectrum to the vibrations of individual amino acid residues. On this basis, detailed information has been obtained about structural changes involving the retinylidene chromophore and protein during the bR photocycle. This includes a determination of the protonation state of the four membrane-embedded Asp residues, identification of specific structurally active amino acid residues, and the detection of protein secondary structural changes. This information is being used to develop an increasingly detailed picture of the bR proton pump mechanism. |
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Keywords: | Proton transport biomembranes infrared membrane protein energy transduction |
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