Molecular Mechanisms of Bacterial Bioluminescence.

Bioluminescence refers to the production of light by living organisms. Bioluminescent bacteria with a variety of bioluminescence emission characteristics have been identified in , and . Bioluminescent bacteria are mainly found in marine habitats and they are either free-floating, sessile or have specialized to live in symbiosis with other marine organisms. On the molecular level, bioluminescence is enabled by a cascade of chemical reactions catalyzed by enzymes encoded by the operon with the gene order . The and genes encode the α- and β- subunits, respectively, of the enzyme luciferase producing the light emitting species. , and constitute the fatty acid reductase complex, responsible for the synthesis of the long-chain aldehyde substrate and encodes a flavin reductase. In bacteria, the heterodimeric luciferase catalyzes the monooxygenation of long-chain aliphatic aldehydes to the corresponding acids utilizing reduced FMN and molecular oxygen. The energy released as a photon results from an excited state flavin-4a-hydroxide, emitting light centered around 490 nm. Advances in the mechanistic understanding of bacterial bioluminescence have been spurred by the structural characterization of protein encoded by the operon. However, the number of available crystal structures is limited to LuxAB (), LuxD () and LuxF (). Based on the crystal structure of LuxD and homology models of LuxC and LuxE, we provide a hypothetical model of the overall structure of the LuxCDE fatty acid reductase complex that is in line with biochemical observations.