Referenced in: none

Automatically associated channels: Slo1

Title: Crystal structures of the L1, L2, N, and O states of pharaonis halorhodopsin.

Authors: Tsutomu Kouyama, Haruki Kawaguchi, Taichi Nakanishi, Hiroki Kubo, Midori Murakami

Journal, date & volume: Biophys. J., 2015 Jun 2 , 108, 2680-90

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/26039169

Abstract
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.