Hypoglycosylation of a brain glycoprotein (β-trace protein) in CDG syndromes due to phosphomannomutase deficiency and N-acetylglucosaminyl-transferase II deficiency

Abstract

Human beta-trace protein is a major intrathecally synthesized polypeptide constituent of human cerebrospinal fluid. We have previously shown that this protein is almost quantitatively modified with biantennary complex-type N-linked oligosaccharides which show "brain-type" glycosylation characteristics (Hoffmann,A. et al., J. Neurochem., 63, pp. 2185-2191, 1994). In the present study human beta-trace protein from the cerebrospinal fluid (CSF) of patients with carbohydrate-deficient glycoprotein syndrome (CDGS) due to phosphomannomutase (PMM) deficiency and N-acetyl-glucosaminyltransferase II (GlcNAc-T II) deficiency as well as from control individuals was studied by Western blot analysis. The protein from pooled CSFs was purified by immunoaffinity chromatography. The protein from the five patients with CDGS PMM deficiency showed three protein bands upon SDS-PAGE analysis corresponding to the di-, mono-, and unglycosylated polypeptide forms. Carbohydrate structural analysis of the enzymatically liberated N-glycans was performed applying mapping by HPAEC-PAD, methylation analysis as well as MALD/TOF-MS. Essentially identical oligosaccharide structures were detected in beta-TP from type I patients and control adult pooled CSF. The beta-trace protein from two patients with GlcNAc-T II deficiency showed a single di-N-glycosylated protein band with a significantly lower molecular weight than the di-glycosylated polypeptide from control patients and the beta-trace protein from pooled adult CSF. Beta-TP from GlcNAc-T II deficiency patients shared only three oligosaccharides out of the 13 observed in beta-TP from controls or patients with PMM deficiency. The major oligosaccharide structures of the glycoprotein from patients with GlcNAc-T II deficiency were found to be monoantennary asialo- or monosialylated lactosamine-type chains with proximal fucose and bisecting GlcNAc.

Band 3 glycoprotein and glycophorin A from erythrocytes of children with congenital disorder of glycosylation type-Ia are underglycosylated

“…Glycans in partly unglycosylated transferrin had normal structures. Similar results were reported for b-trace protein of the cerebrospinal fluid [21]. According to Stibler et al [22], however, hypoglycosylation rather than unglycosylation occurs in serum glycoproteins.…”

In Vivo Specificity of Human α1,3/4-Fucosyltransferases III-VII in the Biosynthesis of LewisX and Sialyl LewisX Motifs on Complex-type N-Glycans

“…In the present paper, we have used stable coexpression of human ␤-TP together with the full-length forms of the five known human ␣1,3/4-FTs from BHK-21 cells in order to assess the in vivo substrate specificity of the different transferases by carbohydrate structural characterization of the secreted ␤-TP using complementary chromatographic and mass spectrometric techniques. Human ␤-TP is a 168-amino acid glycoprotein with two N-glycosylation sites, which has been shown previously to contain peripheral Fuc when the native polypeptide is isolated from human cerebrospinal fluid (27,28) or from human serum (28). By contrast, no peripheral Fuc was found attached to human ␤-TP expressed from BHK-21 cells in a previous study (29).…”

Eukaryotic glycosylation: whim of nature or multipurpose tool?

“…The severity of the symptoms can vary. The responsible genetic abnormality often lies in the gene for phospomannomutase, the enzyme which converts D-mannose-6-phosphate to D-mannose-1-phosphate [513,516,517]. This deficiency causes a disturbance of GDP-D-mannose production, representing an example of impairment in the supply of the activated form of this hexose for N-glycan precursor assembly as Glc 3 Man 9 GlcNAc 2 -P-P-Dol ( fig.…”