Abstract
Polysialoglycoproteins (PSGP) we first isolated from the unfertilized eggs of rainbow trout (Salmo gairderi) and now found to be a ubiquitous component of Salmonidae fish eggs are a novel type of glycoprotein. PSGP from rainbow trout has a molecular weight of 200 X 10(3), a low protein content (about 15% w/w), and a high sialic acid (N-glycolylneuraminic acid (NeuGc] content (about 60%, w/w). In any evaluation of the biological functions of PSGP, information about the complete structure of this unique macromolecular component is relevant. We have now completed the determination of the overall structural organization of the 200-kDa PSGP, and this is the first report of the complete structural analysis of this novel class of glycoprotein: (Asp)0-2-Ala-Thr*-Ser*-Glu-(Ala-Ala-Thr*-Gly-Pro-Ser-Gly-Asp-Asp-Ala-Thr *-Ser*- Glu)n-Ala-Ala-Thr*-Gly-Pro-Ser-Gly where * indicates the amino acid residues to which oligo- and/or polysialylglycan units are attached and n = 25. Thus the most outstanding structural features of PSGP isolated from the unfertilized eggs of rainbow trout are now the occurrence of (a) tandem repeats of a tridecapeptide and (b) an alpha-2----8-linked oligo(poly)sialyl group on each of the core oligosaccharide chains, i.e. GalNAc- beta 1----4(NeuGc alpha 2----3)GalNAc beta 1----3Gal beta 1----4Gal beta 1----3[----8NeuGc alpha 2)n----6)GalNAc alpha 1----Ser (or Thr), Fuc alpha 1----3GalNAc beta 1----3Gal beta 1----4Gal beta 1----3[----8NeuGc alpha 2)n ----6)GalNAc alpha 1----Ser (or Thr), GalNAc beta 1----3Gal beta 1----4Gal beta 1----3[----8NeuGc alpha 2)n----6)GalNAc alpha 1----Ser (or Thr), Gal beta 1----4Gal beta 1----3[----8NeuGc alpha 2)n----6)GalNAc alpha 1----Ser (or Thr), and Gal beta 1----3[----8NeuGc alpha 2)n----6) GalNAc alpha 1----Ser (or Thr).
Highlights
PSGP from rainbow trout has a molecular weight of of the core protein must be determined
We found that 200-kDa PSGP displays rapid and amino acid residues to whicholigo- and/or polysialyl- dramatic change in its molecular size to 9-kDa PSGP upon glycan units are attached and n = 25
GP4"The amino acid composition of GP4 given in Table I indicated that this glycopeptide is composed of the core peptide (Thr/Ser/Pro/Gly/Ala = 1:1:1:2:2)
Summary
COMPLETESTRUCTUREOF 200-kDa POLYSIALOGLYCOPROTEIN FROM THE UNFERTILIZED EGGS OF RAINBOW TROUT (SALMO GAIRDNERI)*. We have established the entireamino and ( b ) ana-Z+S-linkedoligo(po1y)sialylgroup on acid sequence of 9-kDa PSGP tobe Asp-Asp-Ala-Thr*-Ser*-. 6)GalNAcarl~Ser (or Thr), GalNAcBl+ 3GaV1+ 4GalBl+ 3((- SNeuGcaZ),+6)GalNAcal+ Ser (or (200- to 9-kDa) of PSGP [15] prompted us to initiate the present study, and we have firmly established that the 200-. 1960, Warren [2] showed the presence of a vast amount of unbound N-acetylneuraminic acid in trout eggs.) PSGP is a large ( M , 100-200 X lo3)intracellular glycoprotein that contains more than 60% (w/w) sialic acid mostly in the form of oligo(po1y)sialylgroups, (+8NeuGca2+), [1,3,4,5,6,7,8,9,10,11,12].
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