Detection of hypo-N-glycosylation using mass spectrometry of transferrin.
Many congenital disorders of glycosylation (CDG) can be diagnosed by observing the extent of glycosylation of the abundant serum glycoprotein transferrin (Trf). Trf is an N-glycosylated protein with two asparagine glycation sites. CDG types I are those genetic defects which occur prior to transfer of the complex oligosaccharide to the acceptor asparagine in the cotranslated polypeptide chain. CDG Ia constitutes by far the most frequent form of CDG and is the result of mutations in the phosphomannomutase gene. CDG Ia and the Ib subtype (Phosphomannoisomerase deficiency) result in low cellular mannose-1-phosphate levels, a required precursor for oligosaccharide assembly in the endoplasmic reticulum. The deficiency in oligosaccharides with branched mannose structures is thereafter expressed by the appearance of glycoproteins with unoccupied N-glycosylation sites (hypoglycosylation). Currently, there have been at least 11 Type I defects, type Ia being by far the most frequently occurring. Most, if not all type I defects result in unoccupied N-glycation sites. Hypoglycosylated Trf, also known as carbohydrate-deficient Trf (CDT), can be detected using mass spectrometry (MS) to measure the masses of the serum Trf. The methods for sample preparation using affinity chromatography and MS analysis are described in this unit.
O'Brien
John F
JF
Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
Lacey
Jean M
JM
Bergen
H Robert
HR
D002239:Carbohydrate Metabolism, Inborn Errors / Q000175:diagnosis*; D006031:Glycosylation; D006801:Humans; D013058:Mass Spectrometry; D014168:Transferrin / Q000031:analogs & derivatives* / Q000032:analysis
D014168:Transferrin; C056759:carbohydrate-deficient transferrin