Abstract
It was previously shown that reductive alkali treatment of purified human cervical mucin releases a heterogeneous population of reduced neutral, sialylated, and sulfated oligosaccharides (Yurewicz, E. C., and Moghissi, K. S. (1981) J. Biol. Chem. 256, 11895-11904). Four major sialylated oligosaccharide fractions were isolated with approximate compositions of Fuc:GlcNac:Gal:NeuAc:N-acetylgalactosaminitol (GalNAcol) = 0:0:0:1:1 (B1a), 0:0:1:1:1 (B2b), 0:1:2:1:1 (B3a), and 1:1:2:1:1 (B4a), where Fuc is fucose. They comprised roughly 3, 11, 7, and 6% of recovered oligosaccharide chains, respectively. On the basis of periodate oxidations, methylation analyses, and sequential degradations with glycosidases, the following structures were determined. (Formula: see text) Oligosaccharides 1 and 2 are characterized by the presence of N-acetylneuraminic acid in alpha 2,6-linkage to N-acetylgalactosaminitol. The remaining oligosaccharides contain N-acetylneuraminic acid in alpha 2,3-linkage to galactose residues. Oligosaccharides 3 and 4 and oligosaccharides 5 and 6 were isolated as unresolved isomeric mixtures in fractions B3a and B4a, respectively. Oligosaccharides 3 and 4 were distinguished on the basis of susceptibility to digestion with Aspergillus niger beta-galactosidase whereas oligosaccharides 5 and 6 were distinguished on the basis of differential rates of digestion with beef kidney alpha-fucosidase. The structural data indicate the presence of at least two sialyltransferases in human cervical epithelium and further suggest a potential physiologically significant competition between sialyltransferase and beta-N-acetylglucosaminyltransferase for C-6 of the N-acetylgalactosamine residue O-glycosidically linked to serine/threonine of the polypeptide core.
Highlights
It was previously shown that reductive alkali treatment of purified human cervical mucin releases a heterogeneous population of reduced neutral, sialylated, andsulfated oligosaccharides
Biophysical studies of human cervical mucin suggest the presence of linear flexible chains with M, values of10-15 x IO6 whichyield M, 2-3 X IO6 subunits following reduction of disulfide bonds [7, 8].Carbohydrate, which accounts for approximately 70% of the mass of purified human cervical mucin, is present in the form of a heterogeneous population of 0-linked neutral, sialylated, and sulfated oligosaccharides which are asymmetrically distrib
The larger neutraland sialylated human cervical mucin oligosaccharides are based on athird type of inner core structure, namely GlcNAc@1-6(Gal~l-3)GalNAcoTl.he strucmine attached to serine or threoninewhereas in premenstrual tural data,suggest a potentially critical competition mucin sialic acidwas found in a2,3-linkage to peripheral between sialyltransferase and 8-N-acetylglucosaminyl transgalactose residues
Summary
It was previously shown that reductive alkali treatment of purified human cervical mucin releases a heterogeneous population of reduced neutral, sialylated, andsulfated oligosaccharides The structural data indicate the presence of at least two sialyltransferasesin human cervical epithelium and furthersuggest a potential physiologically significant competition between sialyltransferase and 8-N-acetylglucosaminyltransferasfeor C-6 of the Nacetylgalactosamine residue O-glycosidically linked to serinelthreonine of the polypeptide core.
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