TitleBlue protein with red fluorescence.
Publication TypeJournal Article
Year of Publication2016
AuthorsGhosh S, Yu C-L, Ferraro DJ, Sudha S, Pal SKumar, Schaefer WF, Gibson DT, Ramaswamy S
JournalProc Natl Acad Sci U S A
Date Published2016 10 11
KeywordsBiliverdine, Crystallography, X-Ray, Fluorescence, Models, Molecular, Proteins, Recombinant Proteins

The walleye (Sander vitreus) is a golden yellow fish that inhabits the Northern American lakes. The recent sightings of the blue walleye and the correlation of its sighting to possible increased UV radiation have been proposed earlier. The underlying molecular basis of its adaptation to increased UV radiation is the presence of a protein (Sandercyanin)-ligand complex in the mucus of walleyes. Degradation of heme by UV radiation results in the formation of Biliverdin IXα (BLA), the chromophore bound to Sandercyanin. We show that Sandercyanin is a monomeric protein that forms stable homotetramers on addition of BLA to the protein. A structure of the Sandercyanin-BLA complex, purified from the fish mucus, reveals a glycosylated protein with a lipocalin fold. This protein-ligand complex absorbs light in the UV region (λ of 375 nm) and upon excitation at this wavelength emits in the red region (λ of 675 nm). Unlike all other known biliverdin-bound fluorescent proteins, the chromophore is noncovalently bound to the protein. We provide here a molecular rationale for the observed spectral properties of Sandercyanin.

Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID27688756
PubMed Central IDPMC5068307