Infrared fluorescent proteins refer to a class of fluorescent proteins that emit infrared light. Because infrared light can easily pass through body tissue, researchers can track individual molecules in small living animals by labeling them with infrared fluorescent proteins.
Development history of infrared fluorescent proteins
Fluorescent proteins have lit up biology labs more than a decade ago by emitting light in response to everything, including gene expression inside cells and the presence of anthrax and other biological warfare agents.
The infrared fluorescent protein is a modified version of a protein found in D. radiodurans, known for its ability to survive large doses of radiation. Scientists previously discovered that a protein in the bacteria, a phytochrome, absorbs deep red light at the far end of the visible spectrum. It can use this energy to send signals that cause cells to turn on certain genes.
In 2008, Roger Tsien, a biochemist at the University of California, San Diego, and a Nobel Laureate in Chemistry, and his team rewrote the genetic code of phytochrome and cut off the part responsible for sending biochemical signals. . The result was a class of infrared fluorescent proteins, but these proteins were only able to emit weak infrared light. So the researchers mutated the improved phytochrome gene for several more rounds, and then selected the one with the strongest light-emitting ability. The new fluorescent protein is four times as powerful as the original version.
On May 8, 2009, the research team reported the findings in the journal Science. The researchers also inserted the gene for the new fluorescent protein into an adenovirus that infects the livers of mice. After injecting the virus into the tail veins of mice, they found infrared fluorescence in the rodents’ livers 5 days later.
Infrared fluorescent protein action
The findings are “an important step in the right direction,” says John Frangioni, a fluorescence imaging expert at Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, Massachusetts. Researchers can use this technique to probe the extent of disease, such as cancer, at the molecular level. But Frangioni emphasizes that much of the infrared light emitted by the new fluorescent proteins is still blocked by animal tissue, so researchers also need to look for fluorescent proteins that emit longer wavelengths of infrared light. Tsien thinks this is entirely possible because the genetic database already contains more than 1,500 bacterial proteins similar to phytochromes. So the next job is to figure out whether one of these fluorescent proteins can hit the most efficient “hitting spot” in biology.