Matthew Ranaghan - Green Proteorhodopsin Reconstituted into Nanoscale Phospholipid Bilayers (Nanodiscs) as Photoactive Monomers

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  Publication Details (including relevant citation   information):

  Ranaghan, M. J., Schwall, C. T., Alder, N. N., Birge, R. R

  J. Am. Chem. Soc., 2011, 133 (45), pp 18318–18327

  DOI: 10.1021/ja2070957


  Over 4000 putative proteorhodopsins (PRs) have been identified   throughout the oceans and seas of the Earth. The first of these   eubacterial rhodopsins was discovered in 2000 and has expanded   the family of microbial proton pumps to all three domains of   life. With photophysical properties similar to those of   bacteriorhodopsin, an archaeal proton pump, PRs are also   generating interest for their potential use in various photonic   applications. We perform here the first reconstitution of the   minimal photoactive PR structure into nanoscale phospholipid   bilayers (nanodiscs) to better understand how protein–protein and   protein–lipid interactions influence the photophysical properties   of PR. Spectral (steady-state and time-resolved UV–visible   spectroscopy) and physical (size-exclusion chromatography and   electron microscopy) characterization of these complexes confirms   the preparation of a photoactive PR monomer within nanodiscs.   Specifically, when embedded within a nanodisc, monomeric PR   exhibits a titratable pKa (6.5–7.1) and   photocycle lifetime (100–200   ms) that are comparable to the detergent-solubilized protein.   These ndPRs also produce a photoactive blue-shifted absorbance,   centered at 377 or 416 nm, that indicates that protein–protein   interactions from a PR oligomer are required for a fast   photocycle. Moreover, we demonstrate how these model membrane   systems allow modulation of the PR photocycle by variation of the   discoidal diameter (i.e., 10 or 12 nm), bilayer thickness (i.e.,   23 or 26.5 Å), and degree of saturation of the lipid acyl chain.   Nanodiscs also offer a highly stable environment of relevance to   potential device applications.

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