lumazine synthase (6,7-dimethyl-8-ribityllumazine synthase, LS), catalyzes the penultimate step in the biosynthesis of riboflavin (vitamin B2); type-I
Type-I LS, also known as RibH1, catalyzes the penultimate step in the biosynthesis of riboflavin in plants and microorganisms. LS catalyse the formation of 6,7-dimethyl-8-ribityllumazine by the condensation of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione with 3,4-dihydroxy- 2-butanone-4-phosphate. Subsequently, the lumazine intermediate dismutates to yield riboflavin and 5-amino-6-ribitylamino- 2,4(1H,3H)-pyrimidinedione, in a reaction catalyzed by riboflavin synthase synthase (RS); RS belongs to a different family of the Lumazine-synthase-like superfamily. Riboflavin is the precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) which are essential cofactors for the catalysis of a wide range of redox reactions. These cofactors are also involved in many other processes involving DNA repair, circadian time-keeping, light sensing, and bioluminescence. Riboflavin is biosynthesized in plants, fungi and certain microorganisms; as animals lack the necessary enzymes to produce this vitamin, they acquire it from dietary sources. Type II LSs are distinct from type-I LS not only in protein sequence, but in that they exhibit different quaternary assemblies; type-I LSs form pentamers. The pathogen Brucella spp. encode both a Type-I LS and a Type-II LS called RibH1 and RibH2, respectively. RibH1/type-I LS appears to be the functional LS in Brucella spp., whereas RibH2/type-II LS has much lower catalytic activity as LS. The pathogen Brucella spp. have both a type-I LS and a type-II LS called RibH1 and RibH2, respectively. RibH1/type-I LS appears to be a functional LS in Brucella spp., whereas RibH2/type-II LS has much lower catalytic activity as LS.
Comment:Type I LSs form homopentamers, each pentamer contains 5 active sites which are located at the interfaces between adjacent monomers.
Structure:1EJB_A/B/C/D/E; Saccharomyces cerevisiae LS homopentamer binds a phosphonate intermediate analogue, 5-(6-D-ribitylamino-2,4-dihydroxypyrimidine-5-yl)-1-pentyl-phosphonic acid; contacts at 4A
Comment:the intermediate analogue mimics the hypothetical Schiff's base intermediate of the enzyme catalyzed reaction
Jiyao W et al.(2023). "The conserved domain database in 2023.",