4qry

Publication Abstract from PubMed

Halorhodopsin from Natronomonas pharaonis (pHR) functions as a light-driven halide ion pump. In the presence of halide ions, the photochemical reaction of pHR is described by the scheme: K--> L1 --> L2 --> N --> O --> pHR' --> pHR. Here, we report light-induced structural changes of the pHR-bromide complex observed in the C2 crystal. In the L1-to-L2 transition, the bromide ion that initially exists in the extracellular vicinity of retinal moves across the retinal Schiff base. Upon the formation of the N state with a bromide ion bound to the cytoplasmic vicinity of the retinal Schiff base, the cytoplasmic half of helix F moves outward to create a water channel in the cytoplasmic interhelical space, whereas the extracellular half of helix C moves inward. During the transition from N to an N-like reaction state with retinal assuming the 13-cis/15-syn configuration, the translocated bromide ion is released into the cytoplasmic medium. Subsequently, helix F relaxes into its original conformation, generating the O state. Anion uptake from the extracellular side occurs when helix C relaxes into its original conformation. These structural data provide insight into the structural basis of unidirectional anion transport.

Crystal Structures of the L1, L2, N, and O States of pharaonis Halorhodopsin.,Kouyama T, Kawaguchi H, Nakanishi T, Kubo H, Murakami M Biophys J. 2015 Jun 2;108(11):2680-90. doi: 10.1016/j.bpj.2015.04.027. PMID:26039169^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.