A great story in the news this week had to do with bioluminescence: Scientists have shown for the first time that deep-sea fish that use bioluminescence for communication are diversifying into different species faster than other glowing fish that use light for camouflage. The new research indicates that bioluminescence – a phenomenon in which animals generate visible light through a chemical reaction – could promote communication and mating in the open ocean, an environment with few barriers to reproduction.
Based on such an interesting story, and in particular – during this International Year of Crystallography – we thought it would be neat to look at how the proteins that cause bioluminescence in fish, fireflies, click beetles and other living organisms are studied by scientists and for what applications. Each bioluminescent species produces its own slight variation of the luciferase molecule, based on slight changes in the peptide sequence in the protein. Each protein is made of several hundred peptide units, which means each protein is composed of thousands of atoms. To understand the differences in luciferase molecules between species, scientists must be able to probe the atomic level. For protein crystallography experiments, scientists use high-intensity X-ray beams produced in facilities called synchrotrons. In comparison to the visible light that our eyes can see, X-rays are also a type of light, except that X-ray photons are very high energy and have short wavelengths. The wavelength of an X-ray is about the size of the distance between two atoms in a molecule, which is key when trying to determine the structure of a luciferase protein. But first, a protein crystallographer studying luciferase has to remove the molecules from solution (the cytoplasm of the bioluminescent cells). By doing so, scientists grow tiny crystals of luciferase proteins, where the molecules are tightly packed into crystalline structures that would not form under natural conditions.
Within a cell, luciferase molecules mix with luciferin molecules in an enzyme-substrate complex to create the amazing blues and greens we see emitted by so many of nature’s wonderful creatures. In fact, the chemical reactions that occur for bioluminescence based on the luciferase-luciferin system represent some of the most efficient reactions in nature. The efficiency of a chemical reaction or process can be measured in terms of energy: more efficient reactions and processes return a greater fraction of the energy initially put into the system to drive it forward. For example, in comparison to a bioluminescent reaction, which tends to be 80-90% efficient (a return of 80-90% of the energy put into the reaction), using an incandescent bulb as a light source is poorly efficient. In the case of the incandescent bulb, only 10% of the energy is used to create light. The other 90% is essentially “lost” as heat, which also explains why incandescent bulbs are so hot to the touch!
Clearly, luciferase proteins have a lot to offer scientists, some of whom are already evaluating these molecules for use as possible eco-friendly light sources in the future. Luciferase also has already been used to help investigators at crime scenes uncover traces of blood, as well as by blood banks to determine the viability of red blood cells. (Photo credit: Thinkstock)