Studies on the reaction mechanism of riboflavin synthase: X-ray crystal structure of a complex with 6-carboxyethyl-7-oxo-8-ribityllumazine.
Riboflavin synthase catalyzes the disproportionation of 6,7-dimethyl-8-ribityllumazine affording riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. We have determined the structure of riboflavin synthase from Schizosaccharomyces pombe in complex with the substrate analog, 6-carboxyethyl-7-oxo-8-ribityllumazine at 2.1 A resolution. In contrast to the homotrimeric solution state of native riboflavin synthase, we found the enzyme to be monomeric in the crystal structure. Structural comparison of the riboflavin synthases of S. pombe and Escherichia coli suggests oligomer contact sites and delineates the catalytic site for dimerization of the substrate and subsequent fragmentation of the pentacyclic intermediate. The pentacyclic substrate dimer was modeled into the proposed active site, and its stereochemical features were determined. The model suggests that the substrate molecule at the C-terminal domain donates a four-carbon unit to the substrate molecule bound at the N-terminal domain of an adjacent subunit in the oligomer.
Gerhardt
Stefan
S
Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried, Germany. gerhardt@biochem.mpg.de
Schott
Ann-Kathrin
AK
Kairies
Norman
N
Cushman
Mark
M
Illarionov
Boris
B
Eisenreich
Wolfgang
W
Bacher
Adelbert
A
Huber
Robert
R
Steinbacher
Stefan
S
Fischer
Markus
M
D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011621:Pteridines / Q000737:chemistry / Q000378:metabolism*; D012258:Riboflavin Synthase / Q000737:chemistry / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000201:enzymology; D017386:Sequence Homology, Amino Acid
C473071:6-carboxyethyl-7-oxo-8-ribityllumazine; D011621:Pteridines; D012258:Riboflavin Synthase