Borrowed Proteins in Bacterial Bioluminescence

A library of Photobacterium phosphoreum DNA was screened in λ2001 for the lumazine protein gene, using two degenerate 17-mer oligonucleotide probes that were deduced from a partial protein primary sequence. The lumazine protein gene was localized to a 3.4-kilobase BamHI/EcoRI fragment in one clone. The fragment contained an open reading frame, encoding a 189-residue protein, that had a predicted amino acid sequence that concurred with the partial sequence determined for lumazine protein. Considerable sequence similarity was detected between lumazine protein, the yellow fluorescence protein from Vibrio fischeri, and the α subunit of riboflavin synthetase (EC 2.5.1.9). A highly conserved sequence in lumazine protein corresponds to the proposed lumazine binding sites in the α subunit of riboflavin synthetase. Several secondary structure programs predict the conformation of this site in lumazine protein to be a β-sheet. A minimal model with three interactions between the ligand and this β-sheet structure is proposed, which is consistent with the results of NMR and ligand binding studies.