3vvk
An M-like Reaction State of the azide-bound purple form of pharaonis halorhodopsinAn M-like Reaction State of the azide-bound purple form of pharaonis halorhodopsin
Structural highlights
FunctionBACH_NATPH Light-driven anion pump. Binding affinity for the anions is in the order, bromide > chloride > nitrate > azide > bromate and binding is pH dependent. Publication Abstract from PubMedHalorhodopsin 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 ( approximately 4 A) 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. Large deformation of helix F during the photoreaction cycle of Pharaonis halorhodopsin in complex with azide.,Nakanishi T, Kanada S, Murakami M, Ihara K, Kouyama T Biophys J. 2013 Jan 22;104(2):377-85. doi: 10.1016/j.bpj.2012.12.018. PMID:23442859[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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