3LBW:
reference: Structure and mechanism of proton transport through the transmembrane tetrameric M2 protein bundle of the influenza A virus., Acharya R, Carnevale V, Fiorin G, Levine BG, Polishchuk AL, Balannik V, Samish I, Lamb RA, Pinto LH, DeGrado WF, Klein ML, Proc Natl Acad Sci U S A. 2010 Aug 24;107(34):15075-80. Epub 2010 Aug 5. PMID: 20689043

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