3L8L:
reference: The first crystal structure of a gramicidin complex with sodium: high-resolution study of a nonstoichiometric gramicidin D-NaI complex., Olczak A, Glowka ML, Szczesio M, Bojarska J, Wawrzak Z, Duax WL, Acta Crystallogr D Biol Crystallogr. 2010 Aug;66(Pt 8):874-80. Epub 2010, Jul 9. PMID: 20693686

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