Luciferase gene of a Caribbean fireworm (Syllidae) from Puerto Rico.

The fireworms Odontosyllis spp. are globally distributed and well-known for their characteristic and fascinating mating behavior, with secreted mucus emitting bluish-green light. However, knowledge about the molecules involved in the light emission are still scarce. The fireworms are believed to emit light with a luciferin-luciferase reaction, but biochemical evidence of the luciferase is established for only one species living in Japan and no information is available for its luciferin structure. In this study, we identified a luciferase gene from a related Puerto Rican fireworm. We identified eight luciferase-like genes in this Puerto Rican fireworm, finding amino acid identities between Japanese and Puerto Rican luciferase-like genes to be less than 60%. We confirmed cross reactivity of extracts of the Japanese fireworm luciferin with a recombinant Puerto Rican luciferase (PR1). The emission spectrum of recombinant PR1 was similar to the crude extract of the native luciferase, suggesting that PR1 is a functional luciferase of this Puerto Rican fireworm. Our results indicate that the molecular mechanism of luminescence is widely conserved among fireworms.

Novel application of Macrolampis sp2 firefly luciferase for intracellular pH-biosensing in mammalian cells.

Bioluminescence is widely used in biosensors. Firefly luciferase-based bioluminescent sensors are among the most popular ones. Firefly luciferases are pH-sensitive, displaying a large red shift at acidic pH, a property that has been considered undesirable for most applications. Currently, biosensors that can detect intracellular pH are in demand, and some fluorescent biosensors are available. However, pH sensors using bioluminescence have not been used yet. Thus, we decided to harness a firefly luciferase to measure the intracellular pH in mammalian cells. For this purpose, we engineered the luciferase derived from Macrolampis sp2 firefly to localize it on the cytosol or nucleus, in order to observe pH variation in these compartments during biological activities. We first calibrated the emission ratios (R = Igreen/Ired) at different pH values. As expected, we observed a red shift of light emission under acidic conditions when the cells were subjected to different pH conditions in the presence of the K+/H+ ionophore, nigericin. Based on these results, we concluded that this firefly luciferase can be used as a diagnostic tool for measuring the intracellular pH variation in pathogenic cells or in cells during apoptosis. This is the first example of real time-monitoring of pH change using color tuning luciferase.