Deglycosylation of glucoamylase from Aspergillus niger: effects on structure, activity and stability.

A comparative structure-function study was performed to establish possible roles of carbohydrates in stabilization of glycoproteins, using glucoamylase (GA) as a model system. In addition to kinetic properties, stability toward elevated temperatures, extremes of pH, high salt concentrations together with circular dichroism, intrinsic/extrinsic fluorescence studies, proteolysis and affinity for interaction with hydrophobic ligands were investigated. Related to all the main properties examined, with one exception, glycosylation provided improvement in functional characteristics of the enzyme, especially in relation to its thermostability. Results are explained in terms of provision of stabilizing intermolecular interactions by the sugar molecules. The improvement in protein rigidity together with reduction of surface hydrophobicity appear to be especially important in relation to prevention of aggregation, an important mechanism of irreversible thermoinactivation, occurring at elevated temperatures.