Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/22/2005
Publication Date: 4/22/2005
Citation: Jordan, D.B., Calabrese, J.C. 2005. Active-site models of riboflavin synthase [abstract]. International Symposium on Flavins and Flavoproteins. p. 104. Interpretive Summary:
Technical Abstract: Riboflavin synthase (RS, EC 18.104.22.168) catalyses the mechanistically complex dismutation of two molecules of 6,7-dimethyl-8-(1´-D-ribityl)-lumazine (DMRL) to yield riboflavin and 4-ribitylamino-5-amino-2,6-dihydroxypyrimidine (RAADP). In the event, one butene unit is transferred from the donor DMRL, which becomes RAADP, to the acceptor DMRL, which becomes riboflavin. There is no cofactor requirement for the catalyst and the reaction proceeds without enzyme at neutral pH, although at low rates and yields of riboflavin. On the enzyme, a pentacyclic reaction intermediate has been isolated and shown to be catalytically competent; its breakdown to riboflavin and RAADP was determined to be rate limiting and its stereochemistry was predicted. The first X-ray structure of RS was determined at 2.0 Å resolution for the Escherichia coli enzyme. RS from E. coli, other eubacteria, and eukaryotes is a homotrimer of 23 kDa subunits with each subunit consisting of two similar beta barrels and a C-terminal alpha helix. Monomers assemble asymmetrically to form the trimer, which is stabilized through contacts between residues of the C-terminal alpha helices. Active sites are formed by two beta barrels, each from a separate subunit. Geometrical restraints permit only one active site of the three in the trimer to be formed at a time. More recently, X-ray structures of the Schizosaccharomyces pombe RS monomer, the N-terminal domain of the E. coli RS, and the E. coli trimer have been determined in the presence of analogues of DMRL and riboflavin. This presentation elaborates on the binding modes of the ligands. The results should be useful for better understanding the roles of amino acid residues in the catalytic mechanism and for structure-based design of inhibitors that could have utility as antibacterial, antifungal, and herbicidal properties.