4QRY

Crystal Structures of the L1, L2, N, and O States of pharaonis Halorhodopsin

(2015) Biophys J 108: 2680-2690

• PubMed: 26039169 Search on PubMedSearch on PubMed Central
• DOI: https://doi.org/10.1016/j.bpj.2015.04.027
• Primary Citation of Related Structures:  
  4QRY


• PubMed 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.

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Organizational Affiliation: 

Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan; RIKEN Harima Branch, 1-1-1, Kouto, Sayo, Hyogo, Japan. Electronic address: [email protected].