Malaysian frogs of the species Polypedates leucomystax protect their spawn by secreting a protective liquid and whipping it up to a foam which turns blue after a while. Researchers have now identified the cause of this colour as a highly unusual protein which they named after the similarly coloured cartoon heroes: ranasmurfin (where rana is latin for frog).
Ranasmurfin crystallizes so nicely (forming deep blue crystals) that the researchers didn’t even need to solve the sequence to figure out what they were looking at. They found a novel fold (very rare these days) and a novel cross-link between the two subunits, namely an indophenol group which has never before been observed in a stable protein structure. This group is also the source of the characteristic blue colour. Much like the chromophore in Green Fluorescent Protein, it arises from a chemical reaction between amino acids of the protein chain that occurs after the synthesis is finished. Thus one would not have been able to predict this feature from sequencing the gene.
Unusual Chromophore and Cross-Links in Ranasmurfin: A Blue Protein from the Foam Nests of a Tropical Frog
Muse Oke, Rosalind Tan Yan Ching, Lester G. Carter, Kenneth A. Johnson, Huanting Liu, Stephen A. McMahon, Malcolm F. White, Carlos Bloch Jr., Catherine H. Botting, Martin A. Walsh, Aishah A. Latiff, Malcolm W. Kennedy, Alan Cooper, James H. Naismith
Angewandte Chemie International Edition