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Catalytic Site Atlas

CSA LITERATURE entry for 1luc

E.C. namealkanal monooxygenase (FMN)
SpeciesVibrio harveyi (Bacteria)
E.C. Number (IntEnz)
CSA Homologues of 1luc1brl,3fgc,
CSA Entries With UniProtID P07740
CSA Entries With EC Number
PDBe Entry 1luc
PDBSum Entry 1luc
MACiE Entry M0132

Literature Report

IntroductionIn the bioluminescence reaction catalysed by bacterial luciferase, a flavin-dependent monooxygenase, reduced riboflavin 5' -phosphate (FMNH2 )1 and a long-chain aliphatic aldehyde are oxidized by molecular oxygen to produce FMN, H2 O, aliphatic carboxylic acid, and visible light with an overall quantum yield of about 0.12. It is intriguing that bacterial luciferase is unique among all known flavindependent monooxygenases in catalysing a light-emitting reaction. Vibrio harveyi luciferase is an alpha-beta heterodimer, the proposed earlier to be at a cleft in the alpha subunit.
MechansimThe FMN cofactor undergoes a double bond rearrangement that results in the single electron transfer from FMN to dioxygen and a proton transfer from an unidentified base to the dioxygen molecule.Then the FMN and dioxygen radical species undergo a colligation reaction to form the FMN-peroxo adduct. The carbonyl carbon of the aldehyde substrate deprotonates the peroxo-intermediate, which attacks the carbonyl carbon of the aldehyde substrate in a nucleophilic addition. FMN donates a single electron into the peroxo group, causing a homolysis of the O-O bond. His44 deprotonates the intermediate, causing the C-H bond to homolyse, with a single electron being donates to the oxygen radical and one onto the carbon of the cleaved C-H bond. The bound oxygen on the FMN deprotonates His44. The negatively charged oxygen on the intermediate initiates a single electron transfer from the intermediate to the FMN which then emits a photon. The FMN-bound hydroxyl group initiates an intramolecular elimination of water, generating the product FMN.
Note: There are at least three alternative proposals for the decay of the FMN 4-peroxyhemiacetal intermediate to emit light and yield the final products carboxylic acid FMN and water. A Baeyer-Villiger mechanism involving a hydride transfer from the intermediate. A mechanistic proposal involving a rate-limiting electron transfer to an intermediate dioxirane. And finally a modified version of the chemically initiated electron exchange luminescence which predicts that the oxidation potential of the flavin should affect the rate of bioluminescence reaction and found to be so in experiments with substituted FMN analogs. Mutational studies have shown that residues Phe46A Phe49A Phe114A Phe117A and Phe261A are critical to the luciferase activity due to the fact that their bulky and hydrophobic nature allow shielding of the critical intermediates from exposure to medium. The torsional flexibility of Gly275A in a conserved loop has also been shown to be critical to luciferase activity.

Catalytic Sites for 1luc

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA4444macie:sideChainActs as a general base to deprotonate the intermediate, and then protonates the bound oxygen on FMN.
HisA4545macie:sideChainAids formation of the Flavin 4a-hydroperoxide intermediate.

Literature References

Huang S
Identification and characterization of a catalytic base in bacterial luciferase by chemical rescue of a dark mutant.
Biochemistry 1997 36 14609-14615
PubMed: 9402752
Li H
Effects of mutations of the alpha His45 residue of Vibrio harveyi luciferase on the yield and reactivity of the flavin peroxide intermediate.
Biochemistry 1999 38 4409-4415
PubMed: 10194361