InterPro: IPR001783 Lumazine-binding protein

The following proteins have been shown [1, 2] to be structurally and evolutionary related:

• Riboflavin synthase alpha chain (EC:2.5.1.9) (RS-alpha) (gene ribC in Escherichia coli, ribB in Bacillus subtilis and Photobacterium leiognathi, RIB5 in yeast. This enzyme synthesises riboflavin from two moles of 6,7- dimethyl-8-(1'-D-ribityl)lumazine (Lum), a pteridine-derivative.
• Photobacterium phosphoreum lumazine protein (LumP) (gene luxL). LumP is a protein that modulates the colour of the bioluminescence emission of bacterial luciferase. In the presence of LumP, light emission is shifted to higher energy values (shorter wavelength). LumP binds non-covalently to 6,7-dimethyl-8-(1'-D-ribityl)lumazine.
• Vibrio fischeri yellow fluorescent protein (YFP) (gene luxY). Like LumP, YFP modulates light emission but towards a longer wavelength. YFP binds non-covalently to FMN.

These proteins seem to have evolved from the duplication of a domain of about 100 residues. In its C-terminal section, this domain contains a conserved motif [KR]-V-N-[LI]-E which has been proposed to be the binding site for lumazine (Lum) and some of its derivatives. RS-alpha which binds two molecules of Lum has two perfect copies of this motif, while LumP which binds one molecule of Lum, has a Glu instead of Lys/Arg in the first position of the second copy of the motif. Similarly, YFP, which binds to one molecule of FMN, also seems to have a potentially dysfunctional binding site by substitution of Gly for Glu in the last position of the first copy of the motif.