Riboflavin synthase

Riboflavin synthase is an enzyme that catalyzes the final reaction of riboflavin biosynthesis:

(2) 6,7-dimethyl-8-ribityllumazine → riboflavin + 5-amino-6-ribitylamino-2,4-pyrimidinedione

Structure

Riboflavin synthase is a homotrimer with 23kDa subunits. Each monomer contains two beta-barrels and one α-helix at the C-terminus (residues 186-206.) The monomer folds into pseudo two-fold symmetry, predicted by sequence similarity between the N-terminus barrels (residues 4-86) and the C-terminus barrel (residues 101-184).

Active Site

Two 6,7-dimethyl-8-ribityllumazine molecules are hydrogen bound to each monomer as the two domains are topologically similar. The active site is located in the interface of the substrates between monomer pairs and modeled structures of the active site dimer have been created. Only one of the active sites of the enzyme catalyze riboflavin formation at a time as the other two sites face outward and are exposed to solvent. The amino acid residues involved in hydrogen bonding to the ligand are pictured, participating residues may include Thr148, Met160, Ile162, Thr165, Val6, Tyr164, Ser146, and Gly96 at the C-terminal domain and Ser41, Thr50, Gly 62, Ala64, Ser64, Val103, Cys48, His102 at the N-terminal domain.

<gallery>Image: Hydrogen_Bonding_C-Terminal_Domain.jpg| Hydrogen...
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