High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle

Nature. 1999 Oct 21;401(6755):822-6. doi: 10.1038/44623.


Bacteriorhodopsin is the simplest known photon-driven proton pump and as such provides a model for the study of a basic function in bioenergetics. Its seven transmembrane helices encompass a proton translocation pathway containing the chromophore, a retinal molecule covalently bound to lysine 216 through a protonated Schiff base, and a series of proton donors and acceptors. Photoisomerization of the all-trans retinal to the 13-cis configuration initiates the vectorial translocation of a proton from the Schiff base, the primary proton donor, to the extracellular side, followed by reprotonation of the Schiff base from the cytoplasm. Here we describe the high-resolution X-ray structure of an early intermediate in the photocycle of bacteriorhodopsin, which is formed directly after photoexcitation. A key water molecule is dislocated, allowing the primary proton acceptor, Asp 85, to move. Movement of the main-chain Lys 216 locally disrupts the hydrogen-bonding network of helix G, facilitating structural changes later in the photocycle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriorhodopsins / chemistry*
  • Bacteriorhodopsins / metabolism
  • Crystallography, X-Ray
  • Light
  • Models, Molecular
  • Molecular Sequence Data
  • Photochemistry


  • Bacteriorhodopsins

Associated data

  • PDB/1QKO
  • PDB/1QKP