N-glycan Moieties Research Articles

Microheterogeneity of Serum Glycoproteins in Patients with Chronic Alcohol Abuse Compared with Carbohydrate-deficient Glycoprotein Syndrome Type I

Chronic alcohol abuse alters the normal N-glycosylation of transferrin, producing the carbohydrate-deficient transferrin isoforms. This alteration could be similar to that present in patients with carbohydrate-deficient glycoprotein syndrome type 1 (CDG1). We thus compared the alterations of N-glycans present in patients with alcoholism and patients with CDG1. The N-glycans of serum glycoproteins were compared in sera of patients with alcoholism, patients with CDG1, and controls by two-dimensional electrophoresis, neuraminidase, peptide:N-glycosidase F, and endoglycosidase F2 treatments. A specific antibody directed against the amino acid sequence surrounding the N-432 N-glycosylation site of transferrin was prepared (SZ-350 antibody). In patients with alcoholism, the abnormal transferrin and alpha(1)-antitrypsin isoforms were devoid of a variable number of entire N-glycan moieties and were identical with those present in CDG1. In the serum of patients with alcoholism, this finding was less pronounced than in CDG1. In contrast to CDG1, there was no decrease in clusterin or serum amyloid P in patients with alcoholism. The SZ-350 antibody recognized only transferrin isoforms with one or no N-glycan moieties. Antibodies directed against specific N-glycosylation sites of glycoproteins could be useful for developing more specific immunochemical tests for the diagnosis of chronic alcohol abuse.

Differential glycosylation of the protein (PrP) forming scrapie-associated fibrils

PrP is a glycoprotein found in normal brain. In brain affected by scrapie it forms scrapie-associated fibrils (SAF). PrP from SAF shows considerable heterogeneity of size and charge on two-dimensional gels. It separates into six major regions, the three more acidic regions arising as a result of partial proteolytic degradation. The two more basic higher Mr forms (Mr 34,000 and 29,000) of PrP can be reduced in apparent Mr to a lower Mr form (Mr 25,000) with Peptide-N-glycosidase F. In addition, a series of lectins has been found to bind to PrP. Some bind preferentially to the higher Mr forms whereas others bind more strongly to the lower Mr form. Some of the heterogeneity of PrP is therefore due to differential N-glycosylation. We suggest that one or two N-linked carbohydrate chains are bound to the protein causing some of the differences in Mr. The major cause of heterogeneity of PrP is therefore proteolytic cleavage combined with differential glycosylation at the two potential N-glycosylation sites. The glycolipid moiety attached to PrP may be responsible for some lectin binding to all three bands. Using lectins as a probe to study potential differences in N-glycosylation we have looked at their binding to PrP isolated from SAF, from different strains of scrapie and from different regions of the same brain. No major differences in the N-glycan moieties were found.