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J Biomol NMR (2012) 54:401413 DOI 10.1007/s10858-012-9684-8
ARTICLE
Characterization of the ground state dynamics of proteorhodopsin by NMR and optical spectroscopies
Jochen Stehle Frank Scholz Frank Lhr Sina Reckel
Christian Roos Michaela Blum Markus Braun Clemens Glaubitz
Volker Dtsch Josef Wachtveitl Harald Schwalbe
Received: 28 August 2012 / Accepted: 2 November 2012 / Published online: 17 November 2012 Springer Science+Business Media Dordrecht 2012
Abstract We characterized the dynamics of proteorhodopsin (PR), solubilized in diC7PC, a detergent micelle, by liquid-state NMR spectroscopy at T = 323 K. Insights into the dynamics of PR at different time scales could be obtained and dynamic hot spots could be identied at distinct, functionally relevant regions of the protein, including the BC loop, the EF loop, the N-terminal part of helix F and the C-terminal part of helix G. We further characterize the dependence of the photocycle on different detergents (n-Dodecyl b-D-maltoside DDM; 1,2-diheptanoyl-sn-glycero-3-phosphocholine diC7PC) by ultrafast time-resolved UV/ VIS spectroscopy. While the photocycle intermediates of PR in diC7PC and DDM exhibit highly similar spectral characteristics, signicant changes in the population of these intermediates are observed. In-situ NMR experiments have been applied to characterize structural changes during the
photocycle. Light-induced chemical shift changes detected during the photocycle in diC7PC are very small, in line with the changes in the population of intermediates in the photocycle of proteorhodopsin in diC7PC, where the late O-intermediate populated in DDM is missing and the population is shifted towards an equilibrium of intermediates states (M, N, O) without accumulation of a single populated intermediate.
Keywords Proteorhodopsin Photocycle
Membrane protein dynamics NMR spectroscopy
AbbreviationsPR ProteorhodopsinBR BacteriorhodopsinFT Fourier transformIR InfrareddiC7PC 1,2-diheptanoyl-sn-glycero-3-phosphocholine DDM n-Dodecyl b-D-maltoside
NMR Nuclear magnetic resonanceMES 2-(N-morpholino)ethanesulfonic acid SRII Sensory rhodopsin IIUV Ultra violet
Introduction
Light is one of the most interesting environmental factors; it plays a prominent role in information and energy transfer in nature. It triggers numerous signaling cascades, provides energy directly or indirectly for basically all biological systems and plays a major role in sensing environmental changes and in perception. An amazing variety of systems has evolved that interact with light. One extraordinary example of such a system is the class of membrane-
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