title: Structural basis of charge transfer complex formation by riboflavin bound to 6,7-dimethyl-8-ribityllumazine synthase.
abstract: The amino acid residue tryptophan 27 of 6,7-dimethyl-8-ribityllumazine synthase of the yeast Schizosaccharomyces pombe was replaced by tyrosine. The structures of the W27Y mutant protein in complex with riboflavin, the substrate analogue 5-nitroso-6-ribitylamino-2,4(1H,3H)-pyrimidinedione, and the product analogue 6-carboxyethyl-7-oxo-8-ribityllumazine, were determined by X-ray crystallography at resolutions of 2.7-2.8 A. Whereas the indole system of W27 forms a coplanar pi-complex with riboflavin, the corresponding phenyl ring in the W27Y mutant establishes only peripheral contact with the heterocyclic ring system of the bound riboflavin. These findings provide an explanation for the absence of the long wavelength shift in optical absorption spectra of riboflavin bound to the mutant enzyme. The structures of the mutants are important tools for the interpretation of the unusual physical properties of riboflavin in complex with lumazine synthase.
authors.affiliation: Abteilung Strukturforschung, Max-Planck-Institut für Biochemie, Martinsried, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Koch
authors.forename: Constanze
authors.initials: C
authors.lastname: Breithaupt
authors.forename: StefanIlka
authors.initials: S
authors.lastname: GerhardtHaase
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.forename: Mark
authors.initials: M
authors.lastname: Cushman
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012256:Riboflavin / Q000737:chemistry / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000235:genetics / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; C044822:6,7-dimethyl-8-ribityllumazine synthase; D014364:Tryptophan; D012256:Riboflavin