title: A bilirubin-inducible fluorescent protein from eel muscle.
abstract: The 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 Å revealed a biplanar coordination of bilirubin by reversible π-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.
authors.affiliation: Cell Function Dynamics, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako-city, Saitama 351-0198, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Kumagai
authors.forename: Ryoko
authors.initials: R
authors.lastname: Ando
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Miyatake
authors.forename: Peter
authors.initials: P
authors.lastname: Greimel
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Hirabayashi
authors.forename: Tomomi
authors.initials: T
authors.lastname: Shimogori
authors.forename: Atsushi
authors.initials: A
authors.lastname: Miyawaki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001663:Bilirubin / Q000378:metabolism; D003001:Cloning, Molecular; D004524:Eels / Q000378:metabolism*; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029941:Fish Proteins; D049452:Green Fluorescent Proteins; D001663:Bilirubin