Bacteriorhodopsin: A high-resolution structural view of vectorial proton transport

Richard Neutze, Eva Pebay-Peyroula, Karl Edman, Antoine Royant, Javier Navarro, Ehud M. Landau

Research output: Contribution to journalReview articlepeer-review

155 Scopus citations


Recent 3-D structures of several intermediates in the photocycle of bacteriorhodopsin (bR) provide a detailed structural picture of this molecular proton pump in action. In this review, we describe the sequence of conformational changes of bR following the photoisomerization of its all-trans retinal chromophore, which is covalently bound via a protonated Schiff base to Lys216 in helix G, to a 13-cis configuration. The initial changes are localized near the protein's active site and a key water molecule is disordered. This water molecule serves as a keystone for the ground state of bR since, within the framework of the complex counter ion, it is important both for stabilizing the structure of the extracellular half of the protein, and for maintaining the high pKa of the Schiff base (the primary proton donor) and the low pKa of Asp85 (the primary proton acceptor). Subsequent structural rearrangements propagate out from the active site towards the extracellular half of the protein, with a local flex of helix C exaggerating an early movement of Asp85 towards the Schiff base, thereby facilitating proton transfer between these two groups. Other coupled rearrangements indicate the mechanism of proton release to the extracellular medium. On the cytoplasmic half of the protein, a local unwinding of helix G near the backbone of Lys216 provides sites for water molecules to order and define a pathway for the reprotonation of the Schiff base from Asp96 later in the photocycle. A steric clash of the photoisomerized retinal with Trp182 in helix F drives an outward tilt of the cytoplasmic half of this helix, opening the proton transport channel and enabling a proton to be taken up from the cytoplasm. Although bR is the first integral membrane protein to have its catalytic mechanism structurally characterized in detail, several key results were anticipated in advance of the structural model and the general framework for vectorial proton transport has, by and large, been preserved.

Original languageEnglish (US)
Pages (from-to)144-167
Number of pages24
JournalBiochimica et Biophysica Acta - Biomembranes
Issue number2
StatePublished - Oct 11 2002
Externally publishedYes


  • Bacteriorhodopsin
  • Energy transduction
  • Kinetic crystallography
  • Proton pumping
  • Structural mechanism

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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