3A7K:
reference: Crystal structure of the light-driven chloride pump halorhodopsin from Natronomonas pharaonis., Kouyama T, Kanada S, Takeguchi Y, Narusawa A, Murakami M, Ihara K, J Mol Biol. 2010 Feb 26;396(3):564-79. Epub 2009 Dec 1. PMID: 19961859

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