First Fluorescent Protein in Vertebrate Discovered in Eel: New Human Liver Test Imminent

An endangered eel could save human lives--at least according to a team of scientists. They've discovered that the creature harbors a fluorescent protein that could be used as the basis for a revolutionary new clinical test for bilirubin, a critical indicator of human liver function, hemolysis and jaundice.

The animal is known as the Unagi, a sea-going Japanese freshwater eel that's on the brink of extinction. Young eels enter rivers in small shoals before traveling to lakes and other fresh bodies of water where they stay for several years. After sexual maturity, though, these animals enter the sea.  Because of the effects of global warming and harvesting, the number of eels is declining rapidly.

Almost nothing is known about the biology of this creature, but scientists are aware of at least one stunning attribute. The creature possesses the first fluorescent protein ever to be found in vertebrates; it was thought to only exist in simple animals like jellyfish. That's not to say that the eel actually glows, though. Fluorescent proteins need to be activated by being illuminated.

The protein itself is called UnaG, short for Unagi Green protein. What makes it truly unusual, though, is that in nature it needs a natural chemical in order to activate its powerful green light emissions. This chemical is a molecule, called bilirubin. It's universally used in clinical labs around the world a human blood marker for liver function.

Bilirubin itself is the breakdown product of blood hemoglobin. It's toxic if present in excess in the body, like in the characteristic yellow skin and eye color conditions seen in newborn babies, jaundice and kernicterus.

Intrigued by this attribute, the researchers examined UnaG a bit further. By analyzing the structure of UNaG, they discovered a novel mechanism of fluorescence that enabled bilirubin to bind to UnaG and activate its light emission. This method could eventually be used to check liver health across the globe.

"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," said Atsushi Miyawaki, one of the researchers, in a news release. "Before the discovery of UnaG, I couldn't imagine that basic science could have such an impact on human health. From a simple eel, we found a new path to the clinic."

The findings are published in the journal Cell.