Structural highlights
Function[UNAG_ANGJA] Beta-barrel protein that binds unconjugated bilirubin with high affinity. Excitation of the bilirubin-bound protein gives rise to green fluorescence, both under normoxia and hypoxia. The apoprotein is not fluorescent. Does not emit fluorescence in the presence of ditauro-bilirubin, urobilin or biliverdin.[1] Publication Abstract from PubMedThe fluorescent protein toolbox has revolutionized experimental biology. Despite this advance, no fluorescent proteins have been identified from vertebrates, nor has chromogenic ligand-inducible activation or clinical utility been demonstrated. Here, we report the cloning and characterization of UnaG, a fluorescent protein from Japanese eel. UnaG belongs to the fatty-acid-binding protein (FABP) family, and expression in eel is restricted to small-diameter muscle fibers. On heterologous expression in cell lines or mouse brain, UnaG produces oxygen-independent green fluorescence. Remarkably, UnaG fluorescence is triggered by an endogenous ligand, bilirubin, a membrane-permeable heme metabolite and clinical health biomarker. The holoUnaG structure at 1.2 A revealed a biplanar coordination of bilirubin by reversible pi-conjugation, and we used this high-affinity and high-specificity interaction to establish a fluorescence-based human bilirubin assay with promising clinical utility. UnaG will be the prototype for a versatile class of ligand-activated fluorescent proteins, with applications in research, medicine, and bioengineering. A bilirubin-inducible fluorescent protein from eel muscle.,Kumagai A, Ando R, Miyatake H, Greimel P, Kobayashi T, Hirabayashi Y, Shimogori T, Miyawaki A Cell. 2013 Jun 20;153(7):1602-11. doi: 10.1016/j.cell.2013.05.038. Epub 2013 Jun , 13. PMID:23768684[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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