Structural analysis of trisialylated biantennary glycans isolated from mouse serum transferrin - Characterization of the sequence Neu5Gc(alpha 2-3)Gal(beta 1-3)[Neu5Gc(alpha 2-6)]GlcNAc(beta 1-2)Man

Five variants of mouse serum transferrin (mTf, designated mTf-I to mTf-V) w ith respect to carbohydrate composition have been isolated by DEAE-cellulos e chromatography in the following relative percentages: mTf-I: 0.55; mTf-II : 0.79; mTf-III: 71.80; mTf-VI: 21.90 and mTf-V: 4.96, The primary structur es of the major glycans from mTf-III and mTf-IV were determined by methylat ion analysis and H-1-nuclear magnetic resonance (NMR) spectroscopy. All gly cans possessed a common trimannosyl-N,N'-diacetylchitobiose core. From the glycovariant mTf-III two isomers of a conventional biantennary N-acetyllact osamine type were isolated, in which two N-glycolylneuraminic acid (Neu5Gc) residues are linked to galactose either by a (alpha 2-6) or (alpha 2-3) li nkage. A subpopulation of this glycovariant contains a fucose residue (alph a 1-6)-linked to GlcNAc-1. The structure of the major glycan found in varia nt mTf-IV contained an additional Neu5Gc and possessed the following new ty pe of linkage: Neu5Gc(alpha 2-3)Gal(beta 1-3)[Neu5Gc(alpha 2-6)]GlcNAc(beta 1-2)Man(alpha 1-3). In addition to this glycan, a minor compound contained the same antennae linked to Man(alpha 1-6). In fraction mTf-V, which was f ound to be very heterogeneous by H-1 NMR analysis, carbohydrate composition and methylation analysis suggested the presence of tri'-antennary glycans sialylated by Neu5Gc alpha-2,6- and alpha-2,3-linked to the terminal galact ose residues. In summary, mTf glycans differed from those of other analyzed mammalian transferrins by the presence of Neu5Gc and by a Neu5Gc(alpha 2-6 )GlcNAc linkage in trisialylated biantennary structures, reflecting in mous e liver, a high activity of CMP-Neu5Ac hydroxylase and (alpha 2-6)GlcNAc si alyltransferase. (C) 2000 Elsevier Science B.V. All rights reserved.