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Lumazine protein (LumP) is a fluorescent accessory protein having 6,7-dimethyl- 8-(1'-D-ribityl) lumazine (DMRL) as its authentic chromophore. It modulates the emission of bacterial luciferase to shorter wavelengths with increasing luminous strength. To obtain structural information on the native structure as well as the interaction with bacterial luciferase, we have determined the crystal structures of LumP from Photobacterium kishitanii in complexes with DMRL and its analogues, riboflavin (RBF) and flavin mononucleotide (FMN), at resolutions of 2.00, 1.42, and 2.00 [angstrom]. LumP consists of two [beta] barrels that have nearly identical folds, the N-terminal and C-terminal barrels. The structures of LumP in complex with all of the chromophores studied are all essentially identical, except around the chromophores. In all of the structures, the chromophore is tethered to the narrow cavity via many hydrogen bonds in the N-terminal domain. These are absent in the C-terminal domain. Hydrogen bonding in LumP-FMN is decreased in comparison with that in LumP-RBF because the phosphate moiety of FMN protrudes out of the narrow cavity. In LumP- DMRL, the side chain of Gin65 is close to the ring system, and a new water molecule that stabilizes the ligand is observed near Ser48. Therefore, DMRL packs more tightly in the ligand-binding site than RBF or FMN. A docking simulation of bacterial luciferase and LumP suggests that the chromophore is located close enough for direct energy transfer to occur. Moreover, the surface potentials around the ligand-binding sites of LumP and bacterial luciferase exhibit complementary charge distributions, which would have a significant effect on the interaction between LumP and luciferase. doi: 10.1128/JB.01015-09

Vibrio harveyi NADPH-FMN oxidoreductase Arg203 has been shown to be a critical residue for NADPH recognition and binding. Luminous bacteria have three kinds of NAD(P)H-FMN oxidoreductases (flavin reductases) with different pyridine nucleotide specificities. The NADPH-specific flavin reductase of V. harveyi has a uniquely high preference for NADPH.

The luciferase activity of Xenorhabdus luminescens was examined with respect to response to high oxygen tension. Although the growth rate decreased, 100% oxygen induced a twofold increase in bioluminescence which was attributed to an increase in luciferase synthesis. Concommitant to this was an increase in luciferase-associated superoxide dismutase (SOD) activity. However, tests revealed that luciferase and SOD activity were distinct. Therefore, the results suggest that the luciferase system and SOD are co-induced by high oxygen tension.

The permeability of cyanobacterial gas vesicles was determined by measuring the gradient of oxygen through a suspension of Microcystis sp. gas vesicles. Using oxygen diffusivity through water as a reference point, the diffusivity through gas vesicles occupying 35% of the suspension volume was calculated to be 0.81 that of diffusivity through water. The gas permeability coefficient was shown to be 32 mm per second, while the rate consant for the gas vesicle to fill was 2.4 x 10(super -6) per second. It was concluded that randomly oriented gas vesicles cannot provide a gas-conducting channel.

All strains of Vibrio fischeri as well as Photobacterium phosphoreum and V. logei are able to utilize cyclic adenosine monophosphate (cAMP) as sole carbon and energy source. Cyclic AMP was also required for autoinduction of V. fischeri luminiscence system. Cyclic AMP phosphodiesterase activity occured predominantly in the periplasmic space, a novel location for this enzyme. The activity and location of cAMP phosphodiesterase in these organisms might play a role in the degradation of free cAMP as well as contribute to the specificity of V. fischeri-monocentrid fish symbiosis.