Aborted double bicycle-pedal isomerization with hydrogen bond breaking is the primary event of bacteriorhodopsin proton pumping

Piero Altoè, Alessandro Cembran, Massimo Olivucci, Marco Garavelli

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69 Scopus citations

Abstract

Quantum mechanics/molecular mechanics calculations based on ab initio multiconfigurational second order perturbation theory are employed to construct a computer model of Bacteriorhodopsin that reproduces the observed static and transient electronic spectra, the dipole moment changes, and the energy stored in the photocycle intermediate K. The computed reaction coordinate indicates that the isomerization of the retinal chromophore occurs via a complex motion accounting for three distinct regimes: (i) production of the excited state intermediate I, (ii) evolution of I toward a conical intersection between the excited state and the ground state, and (iii) formation of K. We show that, during stage ii, a space-saving mechanism dominated by an asynchronous double bicycle-pedal deformation of the C10 - C11 - C12 - C13 - C14 - N moiety of the chromophore dominates the isomerization. On this same stage a N - H/water hydrogen bond is weakened and initiates a breaking process that is completed during stage iii.

Original languageEnglish (US)
Pages (from-to)20172-20177
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume107
Issue number47
DOIs
StatePublished - Nov 23 2010

Keywords

  • Photoisomerization
  • Quantum mechanics/molecular mechanics (QM/MM)
  • Retinal proteins

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