2REG:
reference: Crystal structures of the choline/acetylcholine substrate binding protein ChoX from Sinorhizobium meliloti in the liganded and unliganded closed states., Oswald C, Smits SH, Hoing M, Sohn-Bosser L, Dupont L, Le Rudulier D, Schmitt L, Bremer E, J Biol Chem. 2008 Sep 8. PMID: 18779321

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