Saturation–transfer–difference NMR to characterize substrate binding recognition and catalysis of two broadly specific glycoside hydrolases

Saturation–transfer–difference NMR spectroscopy (STD NMR) is used to delineate noncovalent enzyme–substrate interactions of β-glycosidases from Pyrococcus furiosus and Aspergillus fumigatus under binding-only conditions at low temperatures, and during catalysis. Glucopyranosyl and galactopyranosyl moieties display a distinct pattern of multiple contacts with each active site, revealing enzyme-specific elements of recognition and portraying the global binding effect caused by single-site modification of the substrate, at carbon 4. The glucopyranose leaving group of cellobiose or lactose shows small relative STD effects except for the anomeric carbon, particularly in the α-form. Its replacement in β-glucosides by an alcohol leaving group strongly affects sugar binding in the proximal enzyme subsite. A combination of STD effects of substrate and product, produced by the catalytic event or added exogenously, characterizes subsite binding during cellobiose hydrolysis.