Energy transformations early in the bacteriorhodopsin photocycle revealed by DNP-enhanced solid-state NMR
- 22 January 2008
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 105 (3), 883-888
- https://doi.org/10.1073/pnas.0706156105
Abstract
By exploiting dynamic nuclear polarization (DNP) at 90 K, we observe the first NMR spectrum of the K intermediate in the ion-motive photocycle of bacteriorhodopsin. The intermediate is identified by its reversion to the resting state of the protein in red light and by its thermal decay to the L intermediate. The (15)N chemical shift of the Schiff base in K indicates that contact has been lost with its counterion. Under these circumstances, the visible absorption of K is expected to be more red-shifted than is observed and this suggests torsion around single bonds of the retinylidene chromophore. This is in contrast to the development of a strong counterion interaction and double bond torsion in L. Thus, photon energy is stored in electrostatic modes in K and is transferred to torsional modes in L. This transfer is facilitated by the reduction in bond alternation that occurs with the initial loss of the counterion interaction, and is driven by the attraction of the Schiff base to a new counterion. Nevertheless, the process appears to be difficult, as judged by the multiple L substates, with weaker counterion interactions, that are trapped at lower temperatures. The double-bond torsion ultimately developed in the first half of the photocycle is probably responsible for enforcing vectoriality in the pump by causing a decisive switch in the connectivity of the active site once the Schiff base and its counterion are neutralized by proton transfer.Keywords
This publication has 51 references indexed in Scilit:
- 250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMRJournal of Magnetic Resonance, 2007
- Bacteriorhodopsin photocycle at cryogenic temperatures reveals distributed barriers of conformational substatesProceedings of the National Academy of Sciences of the United States of America, 2007
- Structural Changes in the L Photointermediate of BacteriorhodopsinJournal of Molecular Biology, 2007
- Mechanism of Primary Proton Transfer in BacteriorhodopsinStructure, 2004
- Magnetic Resonance Studies of the Bacteriorhodopsin Pump CycleAnnual Review of Biophysics and Biophysical Chemistry, 2002
- Structure of bacteriorhodopsin at 1.55 Å resolutionJournal of Molecular Biology, 1999
- The Predischarge Chromophore in Bacteriorhodopsin: A 15N Solid-State NMR Study of the L PhotointermediateBiochemistry, 1997
- Vibrational spectroscopy of bacteriorhodopsin mutants: light-driven proton transport involves protonation changes of aspartic acid residues 85, 96, and 212Biochemistry, 1988
- Resonance Raman study of intermediates of the halorhodopsin photocycleFEBS Letters, 1987
- Quantitative analysis of resonance Raman spectra of purple membrane from Halobacterium halobium: L550 intermediateBiochemistry, 1983