The model of the binary complex reveals a distinct cavity suitable for aldehyde binding adjacent to the isoalloxazine ring and flanked by other key residues (His 44 and Trp 250) implicated in the active site.īacterial luciferase, a heterodimeric protein constituted of two homologous subunits (α and β), catalyzes the oxidation of reduced flavin mononucleotide and fatty aldehyde in a process that reduces molecular oxygen to water and releases energy in the form of light (∼490 nm). Specifically, the isoalloxazine ring of the flavin mononucleotide interacts with the Ala 74–Ala 75 cis-peptide bond as well as with the Cys 106 side chain in the α subunit of luciferase. The resulting model of the bacterial luciferase–flavin mononucleotide complex is consistent with the experimental data available in the literature. A unique model was sought not only on energetic criteria but also on the geometric requirement that the isoalloxazine ring of the active flavin analogs must assume a common orientation in the luciferase-binding site, an orientation that is also inaccessible to the inactive flavin analog. The resulting databases of energy-ranked feasible conformations of the luciferase complexes with flavin mononucleotide, ω-phosphopentylflavin, ω-phosphobutylflavin, and ω-phosphopropylflavin were filtered according to the structure-activity profile of these analogs. The location of the phosphate moiety was used as the anchor in a flexible docking procedure performed by conformation search by using the Monte Carlo minimization approach.
A model of the luciferase–flavin complex is developed here using flexible docking supplemented by these structural constraints. This information, together with previous structure-activity data for the length of the linker connecting the phosphate group to the isoalloxazine ring represent important characteristics of the luciferase-bound conformation of the flavin mononucleotide. The determined location of the phosphate-binding site close to Arg 107 on the α subunit of luciferase is supported here by point mutagenesis. Although the crystal structure of Vibrio harveyi luciferase has been elucidated, the binding sites for the flavin mononucleotide and fatty aldehyde substrates are still unknown.
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