title: Large deformation of helix F during the photoreaction cycle of Pharaonis halorhodopsin in complex with azide.
abstract: Halorhodopsin from Natronomonas pharaonis (pHR), a retinylidene protein that functions as a light-driven chloride ion pump, is converted into a proton pump in the presence of azide ion. To clarify this conversion, we investigated light-induced structural changes in pHR using a C2 crystal that was prepared in the presence of Cl(-) and subsequently soaked in a solution containing azide ion. When the pHR-azide complex was illuminated at pH 9, a profound outward movement (∼4 Å) of the cytoplasmic half of helix F was observed in a subunit with the EF loop facing an open space. This movement created a long water channel between the retinal Schiff base and the cytoplasmic surface, along which a proton could be transported. Meanwhile, the middle moiety of helix C moved inward, leading to shrinkage of the primary anion-binding site (site I), and the azide molecule in site I was expelled out to the extracellular medium. The results suggest that the cytoplasmic half of helix F and the middle moiety of helix C act as different types of valves for active proton transport.
authors: Graduate School of Science, Nagoya University, Nagoya, Japan.
authors: Taichi
authors: T
authors: Nakanishi
authors: Soun
authors: S
authors: Kanada
authors: Midori
authors: M
authors: Murakami
authors: Kunio
authors: K
authors: Ihara
authors: Tsutomu
authors: T
authors: Kouyama
mesh_terms: D000042:Absorption; D001386:Azides / Q000378:metabolism*; D018360:Crystallography, X-Ray; D025602:Halorhodopsins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D008027:Light; D008958:Models, Molecular; D019633:Natronobacterium / Q000378:metabolism*; D055668:Photochemical Processes / Q000528:radiation effects; D010782:Photolysis / Q000528:radiation effects; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D001386:Azides; D025602:Halorhodopsins; D021122:Protein Subunits