1SL8:
reference: All three Ca2+-binding loops of photoproteins bind calcium ions: The crystal structures of calcium-loaded apo-aequorin and apo-obelin., Deng L, Vysotski ES, Markova SV, Liu ZJ, Lee J, Rose J, Wang BC, Protein Sci 2005 Mar;14(3):663-75. Epub 2005 Feb 2. PMID: 15689515

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