Refined crystal structures of red and green fluorescent proteins from the button polyp Zoanthus

The crystal structure of the red fluorescent protein zRFP574 from Zoanthus sp. 2 at 1.51 Å resolution allowed a detailed description of the chromophore derived from decarboxylation of the aspartate side chain within the chromophore-forming tripeptide Asp-Tyr-Gly. Comparison with the newly determined X-ray structure of the green fluorescent protein zGFP506 from a related Zoanthus species and its mutant zGFP506_N66D in the transitional `green' and mature `red' forms provides new insight into the structural chemistry responsible for the acquisition of red fluorescence.