Fluorescent Properties of Sandercyanin, a Blue Protein Found in the Skin Mucus of Walleye Sander vitreus

The discovery and development of fluorescent proteins at the near-infrared channel have revolutionized several areas of molecular and cell biology.  We report here fluorescent properties of Sandercyanin, a blue protein pigment found in the skin mucus of some Canadian walleye, Sander vitreus.  When excited in the UV at 375nm, sandercyanin fluoresces at 675nm in the far red wavelength with an unusually large Stokes shift of 300 nm.  Sandercyanin exists in nature as a small monomer but quickly oligomerizes to a homo-tetramer of 81 kDa in the presence of its chromatophore, biliverdin, which it binds non-covalently to each monomer.  Because biliverdin is present in most vertebrate cells, fluorescence of sandercyanin in vertebrate cells does not attenuate in time.  We have cloned the gene for sandercyanin and are producing the protein recombinantly in E.coli. Applications for recombinant sandercyanin include genetic tagging, tracking of protein/macromolecule movements in living cells and studying protein-protein interactions.  Further, it can be employed for cancer detection, immunological studies, whole-body imaging and stem cell research.