title: Deformation of helix C in the low temperature L-intermediate of bacteriorhodopsin.
abstract: X-ray and electron diffraction studies of specific reaction intermediates, or reaction intermediate analogues, have produced a consistent picture of the structural mechanism of light-driven proton pumping by bacteriorhodopsin. Of central importance within this picture is the structure of the L-intermediate, which follows the retinal all-trans to 13-cis photoisomerization step of the K-intermediate and sets the stage for the primary proton transfer event from the positively charged Schiff base to the negatively charged Asp-85. Here we report the structural changes in bacteriorhodopsin following red light illumination at 150 K. Single crystal microspectrophotometry showed that only the L-intermediate is populated in three-dimensional crystals under these conditions. The experimental difference Fourier electron density map and refined crystallographic structure were consistent with those previously presented (Royant, A., Edman, K., Ursby, T., Pebay-Peyroula, E., Landau, E. M., and Neutze, R. (2000) Nature 406, 645-648; Royant, A., Edman, K., Ursby, T., Pebay-Peyroula, E., Landau, E. M., and Neutze, R. (2001) Photochem. Photobiol. 74, 794-804). Based on the refined crystallographic structures, molecular dynamic simulations were used to examine the influence of the conformational change of the protein that is associated with the K-to-L transition on retinal dynamics. Implications regarding the structural mechanism for proton pumping by bacteriorhodopsin are discussed.
authors.affiliation: Department of Chemistry and Bioscience, Chalmers University of Technology, Box 462, S-40530 Gothenburg, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Edman
authors.forename: Antoine
authors.initials: A
authors.lastname: Royant
authors.forename: Gisela
authors.initials: G
authors.lastname: Larsson
authors.forename: Frida
authors.initials: F
authors.lastname: Jacobson
authors.forename: Tom
authors.initials: T
authors.lastname: Taylor
authors.forename: David
authors.initials: D
authors.lastname: van der Spoel
authors.forename: Ehud M
authors.initials: EM
authors.lastname: Landau
authors.forename: Eva
authors.initials: E
authors.lastname: Pebay-Peyroula
authors.forename: Richard
authors.initials: R
authors.lastname: Neutze
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D001665:Binding Sites; D003460:Crystallization; D006860:Hydrogen Bonding; D011487:Protein Conformation; D012160:Retina / Q000502:physiology; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D001436:Bacteriorhodopsins