4FPD:
reference: Deprotonation of d96 in bacteriorhodopsin opens the proton uptake pathway., Wang T, Sessions AO, Lunde CS, Rouhani S, Glaeser RM, Duan Y, Facciotti MT, Structure. 2013 Feb 5;21(2):290-7. doi: 10.1016/j.str.2012.12.018. PMID: 23394942

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