Electrospray ionization-mass spectrometric analysis of serum transferrin isoforms in patients with carbohydrate-deficient glycoprotein syndrome.
We previously reported that the carbohydrate-deficient glycoprotein (CDG) syndrome is an asparagine-N-linked sugar chain transfer deficiency [Yamashita et al. (1993) J. Biol. Chem. 268, 5783-5789]. In order to confirm this hypothesis, we applied electrospray ionization-mass spectrometric analysis to transferrin isoforms purified from patients with the CDG syndrome. Transferrin isoforms containing 4, 2, and 0 sialic acid residues, S4, S2, and S0, were separated by Mono Q anion exchange column chromatography from serum of a patient with the CDG syndrome. The molecular masses of S4, S2, and S0 were determined to be 79,570 +/- 5, 77,364 +/- 6, and 75,157 +/- 6 Da by electrospray ionization mass spectrometry (ESI/MS). The differences between S4 and S2, and between S2 and S0 were both in accordance with the molecular mass of a disialylated biantennary sugar chain [Neu5Ac alpha 2-->6Gal beta 1-->4GlcNAc beta 1-->2Man alpha 1-->6(Neu5Ac alpha 2-->6Gal beta 1-->4GlcNAc beta 1-->2Man alpha 1-->3)Man beta 1-->4GlcNAc beta 1-->4GlcNAc] (2,206 Da), showing that S0 is nonglycosylated, and that S4 and S2 carry 2 and 1 mol of asparagine-N-linked sugar chains, respectively. The nonglycosylated asparagine site of S2 was elucidated to be random by high performance liquid chromatography-ESI/MS of a tryptic peptide of reduced and pyridylethylated S2.ESI/MS analysis of transferrin purified through one step from serum is applicable for a definite diagnosis of the CDG syndrome.
Yamashita
K
K
Department of Biochemistry, Sasaki Institute, Tokyo.
Ohkura
T
T
Ideo
H
H
Ohno
K
K
Kanai
M
M
D000595:Amino Acid Sequence; D002239:Carbohydrate Metabolism, Inborn Errors / Q000097:blood*; D002240:Carbohydrate Sequence; D006020:Glycopeptides / Q000097:blood; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D007536:Isomerism; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D013577:Syndrome; D014168:Transferrin / Q000032:analysis* / Q000302:isolation & purification
D006020:Glycopeptides; D006023:Glycoproteins; D014168:Transferrin