2AT9:
reference: The structure of bacteriorhodopsin at 3.0 A resolution based on electron crystallography: implication of the charge distribution., Mitsuoka K, Hirai T, Murata K, Miyazawa A, Kidera A, Kimura Y, Fujiyoshi Y, J Mol Biol 1999 Feb 26;286(3):861-82. PMID: 10024456

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