A-linked glycosylation

There are two conserved A-linked sites (based on the Asn-X-Ser/Thr consensus sequence) in all of the PGIPs that have been studied [10], but while there are four sites of potential A-linked glycosylation in bean PGIP, there are seven such sites in the pear and tomato PGIPs (Fig. 8). 

Munro, S. (2001) What can yeast tell us about A-linked glycosylation in the Golgi apparatus FEBS Letters, 498 (2-3), 223-227. 

The majority of ascomycetous yeasts form cell-wall mannans or ga-lactomannans having main chains of (1— 6)-linked a-D-mannopyrano-syl residues, often substituted at 0-2 by a-linked glycosyl groups. The linkage types in the rest of the side chains vary widely, and can consist of 2-O-substituted a- or /3-D-mannopyranosyl residues, or 3-O-substi-... 

Palacpac, N.Q., Yoshida, S., Sakai, H., Kimura, Y, Fujiyama, K., Yoshida, T., and Seki, T. (1999). Stable expression of human 31,4-galactosyltransferase in plant cells modifies A-linked glycosylation patterns. Proc. Natl. Acad. Sci. U.S.A. 96 4692-M697. 

Here, we delineate the biosynthetic pathways of the most common types of protein glycosylation occurring in the secretory pathway mucin-type O-linked glycosylation, A-linked glycosylation, and the formation of glycosaminoglycans. In addition, we will briefly visit the biosynthesis of some less-common varieties of protein glycosylation. 

FIGURE 15.5 A schematic description of how A-linked glycosylated amino aeids are often prepared by the formation of an amide bond between a glycosyl amine and an aetivated aspartie aeid derivative. 

Imiglucerase is an analog of the human enzyme, (beta)-glucocerebrosidase, a monomeric glycoprotein of 497 amino acids, containing four A/-linked glycosylation sites (MW = 60,430). 

Imperiali B, O Connor SE (1999) Effect of A-linked glycosylation on glycopeptide and glycoprotein structure. Curr Opin Chem Biol 3 643-649... 

Some CO- and post-translational modifications of apo B have been identified but, for the most part, their relevance for apo B secretion and function is not known. Apo BlOO contains at least 20 putative glycosylation sites, and plasma apo B contains 8-10% carbohydrate (by weight) with the carbohydrates attached at both N- and O-linked glycosylation sites. Treatment of chicken hepatocytes with tunicamycin, which inhibits A-linked glycosylation, did not reduce the amount of apo B secreted (M.D. Lane, 1982). In contrast, incubation of HepG2 cells with tunicamycin reduced apo BlOO secretion and increased apo B degradation (Section 7). Nevertheless, the apo B-containing particles that were secreted had normal buoyant density (L. Chan, 2001). 

In a recent investigation of the receptor for FimH E. coll that are responsible for urinary tract infections in humans and other mammals, we determined the gly-cosylation patterns of Uroplakin la (UPIa) and Ib, two glycoproteins that are major components of the inner surface of the bladder (43). Each has a single potential A-linked glycosylation site. 

Glycodelin-A (GdA), is a human amniotic fluid-derived glycoprotein that has potent contraceptive and immunosuppressive activities. GdA has 162 amino acids and there are three potential A-linked glycosylation sites at Asn-28, Asn-63 and Asn-85. Together LC-ES-MS and FAB-MS gave sufficient data to define the site occupancy and the sequences of the A-glycans present on GdA. 

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