1DZE:
reference: Crystal structure of the M intermediate of bacteriorhodopsin: allosteric structural changes mediated by sliding movement of a transmembrane helix., Takeda K, Matsui Y, Kamiya N, Adachi S, Okumura H, Kouyama T, J Mol Biol. 2004 Aug 20;341(4):1023-37. PMID: 15328615

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