6XL3:
reference: The crystal structures of a chloride-pumping microbial rhodopsin and its proton-pumping mutant illuminate proton transfer determinants., Besaw JE, Ou WL, Morizumi T, Eger BT, Sanchez Vasquez JD, Chu JHY, Harris A, Brown LS, Miller RJD, Ernst OP, J Biol Chem. 2020 Jul 23. pii: RA120.014118. doi: 10.1074/jbc.RA120.014118. PMID: 32703899

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