luciferase

Lucifer means "light-bringer", and luciferases are a loose family of enzymes that are used by many organisms to produce light - a phenomenon known as bioluminescence.

They are a "loose" family in the sense that different light-producing enzymes use different substrates and have different structures. The generic term for the luciferase substrate is "luciferin"; which refers to a variety of different chemicals used as cofactors.

There are many examples of luciferases in nature:

• Certain bacteria use a riboflavin (like Vitamin B2) luciferin.
• Jack-o'-lantern mushrooms (Omphalotus olearius) glow in the dark.
• Jamaican click beetles (Pyrophorus plagiophthalamus) have multiple luciferases, each producing a different colour (perhaps evolving towards a more orange shade).
• Dinoflagellates produce yet another luciferase, this one with a beta "clam" fold. The luciferin it uses is a polypyrrole (a non-cyclic porphyrin), derived from chlorophyll.
• Squid use coelenterazine and a luciferase called aequorin. Cephalopods in general use a complex mixture of pigments and luminescence to produce signals.
• Finally, probably the best known example of a luciferase is in the firefly, although it is a symbiotic bacterium that does the work. The protein has a multidomain structure, with at least one rosmann fold to bind its ATP cofactor.

The light can be different colours, depending on the oxidised group. The control of the colour emission is down to both the bound cofactor and the protein environment. In addition, the light produced by the luciferase can be absorbed and reemitted at a different wavelength by another protein. This happens in some deep sea fish that need red light, but have blue-green light producing enzymes.

An example of kind of light "transformation" is the Green Fluorescent Protein : aequorin pairing that is used in jellyfish. Aequorin is the luciferase used by other marine animals, like squid, but GFP is not a luciferase. However, both proteins have been taken up as molecular biology 'tools' to highlight structures and reactions taking place in living cells.

• Molecular evolution of dinoflagellate luciferases, enzymes with three catalytic domains in a single polypeptide Liu et al (2004) PNAS 101 16555-16560
• Darwinian natural selection for orange bioluminescent color in a Jamaican click beetle Stolz et al (2003) PNAS 100 14955-14959

For firefly luciferase, at least, it catalyzes, in the presence of Mg2+, the reaction:

Luciferase is now widely used as a research tool for determining promoter function, i.e. whether a gene get's turned on or not.

Let's say I want to determine what and how the TNF-alpha gene in macrophages responds when I add lipopolysaccharide to them.

I would transfect my macrophages with a reporter construct, a piece of DNA that has the promoter from the TNF-alpha gene. The promoter is the control element of a gene, the part that is involved in the turning on and off of the gene, and not the product of the gene itself. Except in my reporter construct, this TNF-alpha promoter would be controlling the expression of luciferase, instead of TNF-alpha.

Then, I would treat my transfected macrophages with with varying amounts of lipopolysaccharide. The TNF-alpha promoter would get turned on to various degrees. After a set time, I can determine how and if the TNF-alpha promoter responded by determining the amount of luciferase made by the cells (using a luminometer).

This is just an example, of course, you could replace the TNF-alpha promoter with any other natural or artificial promoter, and replace the macrophage with any cell you want to study, and replace the lipopolysaccharide with any stimulus you with to use.

As an additional note, GFP is a totally different kind of protein, and luciferase itself isn't really fluorescent.

Luciferase is an enzyme which uses energy to give off light. GFP, like other fluorescent molecules, just gives off light when excited by light. Basically, if you shine a certain wavelength light at GFP, it emits light at another wavelength.

GFP is still really cool, though.