Explain molecular mechanism of bioluminescence.
Answers
Bioluminescence refers to the production of light by living organisms. Bioluminescent bacteria with a variety of bioluminescence emission characteristics have been identified in Vibrionaceae, Shewanellaceae and Enterobacteriaceae. 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 lux operon with the gene order luxCDABEG. The luxA and luxB genes encode the α- and β- subunits, respectively, of the enzyme luciferase producing the light emitting species. LuxC, luxD and luxE constitute the fatty acid reductase complex, responsible for the synthesis of the long-chain aldehyde substrate and luxG 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 lux operon. However, the number of available crystal structures is limited to LuxAB (Vibrio harveyi), LuxD (Vibrio harveyi) and LuxF (Photobacterium leiognathi). 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.
This research will focus on the fundamental biochemical mechanisms of light emitting systems in marine dinoflagellates (responsible for the "phosphorescence of the sea") and terrestrial Diptera (flies), two major and evolutionarily independent groups of bioluminescent organisms. The biochemical components of the light-emitting reaction of the dinoflagellate Gonyaulax polyedra - the luciferase enzyme (LCF), the luciferin substrate (LH2), a unique tetrapyrrole, and a luciferin binding protein (LBP)- are sequestered in an organelle, the scintillon. LCF consists of three highly conserved and contiguous sequences, each of which is catalytically active. The minimum peptide size necessary for activity and the location of the active site will be determined.