In molecular biology, luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words luciferin and luciferase, for the substrate and enzyme, respectively. Both words are derived from the Latin word lucifer, meaning "lightbearer", which in turn is derived from the Latin words for "light" (lux) and "to bring or carry" (ferre). Luciferases are widely used in biotechnology, for bioluminescence imaging microscopy and as reporter genes, for many of the same applications as fluorescent proteins. However, unlike fluorescent proteins, luciferases do not require an external light source, but do require addition of luciferin, the consumable substrate.
Examples A variety of organisms regulate their light production using different luciferases in a variety of light-emitting reactions. The majority of studied luciferases have been found in animals, including fireflies, and many marine animals such as copepods, jellyfish, and the sea pansy. However, luciferases have been studied in luminous fungi, like the Jack-O-Lantern mushroom, as well as examples in other kingdoms including bioluminescent bacteria, and dinoflagellates.
Firefly and click beetle The luciferases of fireflies – of which there are over 2000 species – and of the other Elateroidea (click beetles and relatives in general) are diverse enough to be useful in molecular phylogeny. In fireflies, the oxygen required is supplied through a tube in the abdomen called the abdominal trachea. One well-studied luciferase is that of the Photinini firefly Photinus pyralis, which has an optimum pH of 7.8. The catalyzed reaction is:
Sea pansy Also well studied is the sea pansy, Renilla reniformis. In this organism, the luciferase (Renilla-luciferin 2-monooxygenase) is closely associated with a luciferin-binding protein as well as a green fluorescent protein (GFP). Calcium triggers release of the luciferin, coelenterazine, from the luciferin binding protein. The substrate is then available for oxidation by the luciferase, where it is degraded to coelenteramide with a resultant release of energy. In the absence of GFP, this energy would be released as a photon of blue light (peak emission wavelength 482 nm). However, due to the closely associated GFP, the energy released by the luciferase is instead coupled through resonance energy transfer to the fluorophore of the GFP, and is subsequently released as a photon of green light (peak emission wavelength 510 nm). The catalyzed reaction is:
Copepod Newer luciferases have recently been identified that, unlike other luciferases, are naturally secreted molecules. One such example is the Metridia coelenterazine-dependent luciferase (MetLuc, A0A1L6CBM1) that is derived from the marine copepod Metridia longa. The Metridia longa secreted luciferase gene encodes a 24 kDa protein containing an N-terminal secretory signal peptide of 17 amino acid residues. The sensitivity and high signal intensity of this luciferase molecule proves advantageous in many reporter studies. Some of the benefits of using a secreted reporter molecule like MetLuc is its no-lysis protocol that allows one to be able to conduct live cell assays and multiple assays on the same cell.
Bacterial Bacterial bioluminescence is seen in Photobacterium species, Vibrio fischeri and Vibrio harveyi. Light emission in some bioluminescent bacteria utilizes 'antenna' such as lumazine protein to accept the energy from the primary excited state on the luciferase, resulting in an excited lulnazine chromophore which emits light that is of a shorter wavelength (more blue), while in others use a yellow fluorescent protein (YFP) with flavin mononucleotide (FMN) as the chromophore and emits light that is red-shifted relative to that from luciferase.
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