Structural basis of charge transfer complex formation by riboflavin bound to 6,7-dimethyl-8-ribityllumazine synthase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• 6,7-dimethyl-8-ribityllumazine synthase is crucial for riboflavin biosynthesis in yeast.
• Understanding enzyme-substrate interactions is key to elucidating metabolic pathways.

Purpose of the Study:

• To investigate the structural and functional impact of substituting tryptophan 27 with tyrosine in Schizosaccharomyces pombe lumazine synthase.
• To characterize the binding of riboflavin and its analogues to the W27Y mutant protein.

Main Methods:

• Site-directed mutagenesis to create the W27Y mutant.
• X-ray crystallography to determine protein structures at 2.7-2.8 A resolution.
• Analysis of protein-ligand interactions and comparison with wild-type enzyme.

Main Results:

• The W27Y mutation alters the interaction between the enzyme and riboflavin, with the phenyl ring of tyrosine showing peripheral contact compared to tryptophan's pi-complex.
• Structural data explains the lack of spectral shifts observed in riboflavin binding to the mutant enzyme.
• The determined structures provide insights into the unusual physical properties of riboflavin-lumazine synthase complexes.

Conclusions:

• The substitution at position 27 significantly affects the binding mode of riboflavin.
• Structural insights from the W27Y mutant aid in understanding riboflavin's properties within the lumazine synthase active site.
• This study offers valuable tools for further research into lumazine synthase function and riboflavin interactions.