PMID: 12911312

 

    Legend: Sugar

Title : Mass spectrometric identification of N- and O-glycosylation sites of full-length rat selenoprotein P and determination of selenide-sulfide and disulfide linkages in the shortest isoform

Abstract :

1. Rat selenoprotein P is an extracellular glycoprotein of 366 amino acid residues that is rich in cysteine and selenocysteine
2. Plasma contains four isoforms that differ principally by length at the C-terminal end
3. Mass spectrometry was used to identify sites of glycosylation on the full-length protein
4. Of the potential N-glycosylation sites , three located at residues 64, 155, and 169 were occupied, while the two at residues 351 and 356 were not occupied
5. Threonine 346 was variably O-glycosylated
6. Thus, full-length selenoprotein P is both N- and O-glycosylated
7. The shortest isoform of selenoprotein P isoform of selenoprotein P, which terminates at residue 244 , was analyzed for selenide-sulfide and disulfide linkages
8. In this isoform , a single selenocysteine and seven cysteines are present
9. Mass spectrometric analysis indicated that a selenide-sulfide bond exists between Sec40 and Cys43
10. Two disulfides were also detected as Cys149-Cys167 and Cys153-Cys156
11. The finding of a selenide-sulfide bond in the shortest isoform is compatible with a redox function of this pair that might be analogous to the selenol-thiol pair near the C terminus of animal thioredoxin reductase
12. The disulfide formed by Cys153-Cys156 also has some characteristics of a redox active pair