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

Human β-trace protein is a major intrathecally synthesizedpolypeptide constituent of human cerebrospinal fluid. We havepreviously shown that this protein is almost quantitativelymodified with biantennary complex-type N-linked oli-gosaccharideswhich show "brain-type" glycosylation characteristics (Hoffmann,A.et al, J. Neurochenu, 63, pp. 2185-2191,1994). In the presentstudy human β-trace protein from the cerebrospinal fluid(CSF) of patients with carbohydrate-deficient glycoprotein syndrome(CDGS) due to phospho-mannomutase (PMM) deficiency and N-acetyl-glucosami-nyltransferaseII (GlcNAc-T II) deficiency as well as from control individualswas studied by Western blot analysis. The protein from pooledCSFs was purified by immunoaffinity chromatography. The proteinfrom the five patients with CDGS PMM deficiency showed threeprotein bands upon SDS-PAGE analysis corresponding to the di-,mono-, and unglycosylated polypeptide forms. Carbohydrate structuralanalysis of the enzymatically liberated N-glycans was performedapplying mapping by HPAEC-PAD, methylation analysis as wellas MALD/TOF-MS. Essentially identical oli-gosaccharide structureswere detected in β-TP from type I patients and controladult pooled CSF. The β-trace protein from two patientswith GlcNAc-T II deficiency showed a single di-N-glycosylatedprotein band with a significantly lower molecular weight thanthe di-glycosylated polypeptide from control patients and theβ-trace protein from pooled adult CSF. β-TP from GlcNAc-TII deficiency patients shared only three oligosaccharides outof the 13 observed in β-TP from controls or patients withPMM deficiency. The major oligosaccharide structures of theglycoprotein from patients with GlcNAc-T n deficiency were foundto be monoanten-nary asialo- or monosialylated lactosamine-typechains with proximal fucose and bisecting GlcNAc. "brain-type" N-glycosylation carbohydrate deficiency glycoprotein syndrome human β-trace protein phosphomannomutase deficiency GlcNAc-transferase II deficiency human cerebrospinal fluid