3vvk

Publication Abstract from PubMed

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 ( 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.