Few organisms are capable of glowing in the dark. Perhaps the best known example is the firefly, a beetle that can emit flashes of yellow-green light when the small molecule D-luciferin is oxidized by the enzyme firefly luciferase. Here we show that a homologous enzyme in fruit flies is also capable of bioluminescence, but only when treated with a rigid synthetic analog of D-luciferin. The discovery of hidden luciferase activity in a nonluminescent insect suggests that the inherent chemistry required for bioluminescence is more common than previously thought, and that the evolution of new enzymatic activities can be directed by the appearance of a new substrate even in the absence of mutation.
Beetle luciferases are thought to have evolved from fatty acyl-CoA synthetases present in all insects. Both classes of enzymes activate fatty acids with ATP to form acyl-adenylate intermediates, but only luciferases can activate and oxidize D-luciferin to emit light. Here we show that the Drosophila fatty acyl-CoA synthetase CG6178, which cannot use D-luciferin as a substrate, is able to catalyze light emission from the synthetic luciferin analog CycLuc2. Bioluminescence can be detected from the purified protein, live Drosophila Schneider 2 cells, and from mammalian cells transfected with CG6178. Thus, the nonluminescent fruit fly possesses an inherent capacity for bioluminescence that is only revealed upon treatment with a xenobiotic molecule. This result expands the scope of bioluminescence and demonstrates that the introduction of a new substrate can unmask latent enzymatic activity that differs significantly from an enzyme’s normal function without requiring mutation.