Firefly Protein Is an Efficient Source of Near-Infrared Light

Researchers from Connecticut College have been experimenting with luciferase enzyme, the stuff that makes the abdomen of fireflies glow, as a potential agent for generation of near-infrared (nIR) light. This was accomplished by labeling a luciferase variant with nIR fluorescent dyes. The method was used to detect small amounts of blood factor Xa, a coagulation factor inhibited by antithrombin III during heparin therapy, hence the idea this this technology might be used to monitor coagulation.
From an abstract in Bioconjugate Chemistry:

Bioluminescence and bioluminescence resonance energy transfer (BRET) are two naturally occurring light emission phenomena that have been adapted to a wide variety of important research applications including in vivo imaging and enzyme assays. The luciferase enzyme from the North American firefly, which produces yellow−green light, is a key component of many of these applications. Recognizing the heightened interest in the potential of near-infrared (nIR) light to improve these technologies, we have demonstrated that spectral emissions with maxima of 705 and 783 nm can be efficiently produced by a firefly luciferase variant covalently labeled with nIR fluorescent dyes. In one case, an outstanding BRET ratio of 34.0 was achieved emphasizing the importance of selective labeling with fluorescent dyes and the efficiency provided by the intramolecular BRET process. Additionally, we constructed a biotinylated fusion protein that similarly produced nIR light. This novel material was immobilized on solid supports containing streptavidin, demonstrating, in principle, that it may be used for receptor-based imaging. Also, the matrix-bound labeled fusion protein was used to measure factor Xa activity at physiological concentrations in blood. We believe this to be the first report of bright nIR light sources produced by chemical modification of a beetle luciferase.

Link: Firefly protein lights pathway to improved detection of blood clots…
Abstract in Bioconjugate Chemistry: Chemically Modified Firefly Luciferase Is an Efficient Source of Near-Infrared Light
Image credit: James Jordan…