Structural basis for stereospecificity to d-amino acid of glycine oxidase from Bacillus cereus ATCC 14579.

Glycine oxidase (GO) is an enzyme that catalyzes the oxidation of the primary and secondary amines of various chemicals, including glycine, and the enzyme has been applied in a variety of fields, such as biosensor and genetically modified glyphosate resistance plants. Here, we report that the gene product of BC0747 from Bacillus cereus (BcGO) shows oxidase activity for glycine and small d-amino acids, such as d-proline and d-alanine. We also determined the crystal structure of BcGO complexed with the FAD cofactor at a 2.36 Å resolution and revealed how the cofactor binds to the deep pocket of the enzyme. We performed the molecular docking calculation of the glycine substrate to the BcGO structure and identified how the carboxyl- and amine-groups of the d-amino acid are stabilized at the substrate binding site. Structural analysis of BcGO also provided information on the structural basis for the stereospecificity of the enzyme to d-amino acids. In addition, we placed the glyphosate molecule, a plant herbicide, at the substrate binding site, and explained how the mutation of Gly51 to arginine enhances enzyme activity.