The effect of partial deglycosylation on the structure of alpha1-acid glycoprotein

Changes in structure of alpha1-acid glycoprotein were followed after deglycosylation with neuraminidase, peptide N-glycohydrolase F or with a mixture of exoglycosidases. Partially deglycosylated preparations of alpha1-acid glycoprotein free of sialic acids, one complete saccharide component, sialic acids and one saccharide component and sialic acids and some of the external saccharides were obtained. The effect of these changes in saccharide components on the glycoprotein structure was studied by temperature perturbation difference spectroscopy, fluorescence spectroscopy, fourth-derivative of absorption spectra and spectra of CD. Partial deglycosylation resulted in transformation of the molecule to a more compact state in which phenylalanyl residues were even more buried, tyrosyl residues became more uniform and tryptophyl residues were less exposed. The content of ordered secondary structures decreased. The thermal stability of the molecule was not significantly affected. Removal of one of the five saccharide components from the native molecule had apparently deeper effect than total desialyzation of the glycoprotein.