Title : Carbohydrate microheterogeneity of rat serotransferrin
Abstract :
Determination of glycan primary structures and characterization of a new type of trisialylated diantennary glycan
A previously established procedure [Regoeczi, E., Chindemi, P.A., Rudolph, J. R., Spik, G. & Montreuil, J. (1987) Biochem
Cell Biol
65, 948-954] was used to isolate from three DEAE-cellulose chromatographic fractions of diferric rat serotransferrin ( rTf ) subpopulations having discernible affinities for concanavalin A ( ConA )
These entities are designated rTf-1 (not retarded by ConA column), rTf-2 (retarded) and rTf-3 (bound)
Each rTf type was found to be endowed with carbohydrate sufficient to account for a single diantennary glycan/protein molecule
Glycan structures were determined on the glycopeptides by employing GLC/MS and 400-MHz 1H-NMR spectroscopy
All glycans possessed a common, trimannosyl-N,N'-diacetylchitobiose core with or without one L-fucose alpha-1,6-linked to the Asn-linked GlcNAc. Asn-linked GlcNAc
However, there were differences in the antennae
Thus, in rTf-3, both antennae were of the disialylated diantennary N-acetyllactosamine type which is frequently encountered in other plasma glycoproteins
However, the alpha-1,3-Man-linked antenna in rTf-1 as well as rTf-2 had the sequence: Neu5Ac(alpha 2-3)Gal(beta 1-3)[Neu5Ac(alpha 2-6)]GlcNAc(beta 1-2)Man.
In addition, the alpha-1,6-Man-linked antenna deviated in rTf-2 from the standard structure by having the sequence: Neu5Ac(alpha 2-3)Gal(beta 1-3)GlcNAc(beta 1-2)Man.
The possible relevance of the above structures to the ConA binding of rTf is discussed
A further preparation, obtained from the most anionic DEAE-cellulose fraction (peak V) or rTf contained several tetrasialylated diantennary glycans whose precise structures remain to be established in future studies