4JFG:
reference: Significant expansion of the fluorescent protein chromophore through the genetic incorporation of a metal-chelating unnatural amino acid., Liu X, Li J, Hu C, Zhou Q, Zhang W, Hu M, Zhou J, Wang J, Angew Chem Int Ed Engl. 2013 Apr 26;52(18):4805-9. doi: 10.1002/anie.201301307., Epub 2013 Mar 28. PMID: 23554162

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