A fluorescent protein found in the seagoing Japanese freshwater eel Unagi could serve as the basis for a new clinical test for the liver function indicator bilirubin, researchers from the RIKEN Brain Science Institute say.
Writing in Cell, RIKEN’s Atsushi Miyawaki, M.D., Ph.D., and his colleagues show that bilirubin—a blood-based biomarker for human liver function—functions as a noncovalent ligand, inducing fluorescence of the protein, UnaG. They also describe the crystal structure of this glow-in-the-dark protein in detail, and demonstrate the clinical potential of this chromogenic ligand-inducible activation. “We used this high-affinity and high-specificity interaction to establish a fluorescence-based human bilirubin assay with promising clinical utility,” Dr. Miyawaki et al., report.
The researchers also note that UnaG is the first fluorescent protein found in vertebrates. Previously, such proteins had only been observed in invertebrates, like jellyfish.
“We believe that UnaG provides an unexpected foothold into several important but currently obscure areas of human health including bilirubin metabolism and muscle physiology during endurance exercise,” Dr. Miyawaki said in a statement. “Before the discovery of UnaG, I couldn’t imagine that basic science could have such a direct impact on human health. From a simple eel, we found a new path to the clinic.”
Unagi, which is considered a culinary delicacy in Japan, is on the brink of extinction there. Dr. Miyawaki and his colleagues hope that in addition to the new clinical assay, their research could potentially inform conservation efforts.
“A bilirubin-inducible fluorescent protein from eel muscle” appeared online in Cell June 13.