CHAPTER 23: Structural Insights from Solid-State NMR into the Function of the Bacteriorhodopsin Photoreceptor Protein
Published:24 Feb 2014
P. J. Judge, G. F. Taylor, L. S. Vermeer, and A. Watts, in Advances in Biological Solid-State NMR: Proteins and Membrane-Active Peptides, ed. F. Separovic and A. Naito, The Royal Society of Chemistry, 2014, pp. 444-458.
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In addition to being a superbly tuned photoreceptor, bacteriorhodopsin (bR) has provided a stable model system for the development of many biophysical methodologies, including solid-state NMR (ssNMR). Here, we review how these developmental approaches have lead to insights into the function of bR and structurally similar retinal-containing integral membrane proteins. Selective labelling of both the chromophore and amino acid residues has enabled the collection of high-resolution structural information (including orientation and distance measurements) for ground-state bR and other photocycle intermediates. ssNMR is complementary to other biophysical methodologies and the data produced have been used to refine crystallographic models, with a particular emphasis on providing sub-Ångstrom resolution of the conformation of the retinal chromophore in different photocycle intermediates. A key goal of ssNMR methodologies has been to enhance the knowledge base of structure–function relationships for bR within its natural lipid environment, with a longer term aim of applying similar methods for other integral membrane proteins. In doing so, ssNMR addresses the major challenge for membrane structural biology, namely to understand the mechanism of action of active, wild-type proteins in a function-supporting membrane.