Affinity chromatography of glycosyltransferases

Surfaces of murine lymphocyte subsets differ in sialylation states and antigen distribution of a major N-linked penultimate saccharide structure

Rat liver beta-galactoside alpha-2,6-sialyltransferase and Vibrio cholerae sialidase were used with cytidine-5'-monophospho-N-acetyl-[3H]neuraminic acid (CMP-[3H]NeuAc) to specifically probe the distribution and sialylation state of Gal beta 1-4GlcNAc residues on N-linked saccharides on the surfaces of murine lymphocytes. The relative extent of exogenous sialyltransferase-mediated sialylation (per cellular protein) was thymocytes greater than T-cells greater than T-cell lymphoma (EL-4) greater than B-cells greater than B-cell lymphoma (AKTB-1b) greater than splenocytes. Prior desialylation increased exogenous resialylation by 23.8-, 13.1-, 7.1-, 7.9-, 7.0-, and 5.3-fold for splenocytes, B-cells, T-cells, EL-4, AKTB-1b, and thymocytes, respectively. Though numerous glycoproteins were labeled, the majority of the Gal beta 1-4GlcNAc residues were detected on a relatively small number of cell surface proteins, many of which are well-defined lymphocyte antigens. Gal beta 1-4GlcNAc residues on thymocytes were found to exist in an undersialylated state on T200 but not on other antigens (e.g., Thy-1). T200 was found to be fully sialylated on mature cells (i.e., hydrocortisone-resistant thymocytes and splenic T-cells), suggesting that its sialylation state is developmentally regulated. These studies indicate that the number, sialylation state, and polypeptide distribution of the penultimate structure, Gal beta 1-4GlcNAc, differ on N-linked saccharides on the surfaces of different lymphocyte populations.

Sialyltransferases as specific cell surface probes of terminal and penultimate saccharide structures on living cells

Rat liver beta-galactoside alpha-2,6-sialyltransferase and Vibrio cholerae sialidase were used, in conjunction with CMP-N-acetyl-[3H]neuraminic acid, to probe the glycoconjugate distribution, sialylation state, and level of penultimate Gal beta 1-4GlcNAc residues on the surfaces of murine thymic lymphocytes. We report a detailed characterization of this sialyltransferase-mediated labeling system. Exogenous sialylation of intact cells is dependent on transferase, sugar nucleotide donor, cell number, and incubation time. Additionally, we have demonstrated that the system labeling the cell surface is noncytotoxic and nonmetabolic and is interacting with the entire cell population. Analysis of the exosialylated structures indicates that the sialyltransferase specifically produces an alpha 2-6 linkage on N-linked oligosaccharides. Using this labeling system, we have probed the cell surface saccharide structures of murine thymocytes and demonstrated that most Gal beta 1-4GlcNAc residues are sialylated in the native state. However, one antigen, T200 (Ly-5), is strikingly undersialylated when compared to other cell surface glycoproteins (e.g., Thy 1.2). Upon analysis of exogenously sialylated oligosaccharides, labeled sialic acid was found almost exclusively on monosialylated structures with the remainder on bisialylated oligosaccharides. This suggests that the purified sialyltransferase is very precise in its recognition of oligosaccharides present on the surface of living thymic lymphocytes. This paper illustrates the combined uses of specific glycosidases and glycosyltransferases and how they can be employed in the detailed study of selected cell surface saccharide structures on living nucleated cells.

Purification and separation of two soluble fucosyltransferase activities of small intestinal mucosa

1. Rat small intestinal soluble fucosyltransferase is purified more than 2000-fold using chromatographic procedures with DEAE-cellulose, CM-cellulose, GDP-Sepharose and Concanavalin A-Sepharose. 2. Chromatography on Sephadex G15 of the final enzymatic fraction clearly separates two activities: a first peak incorporates fucose on asialoserotransferrin and a second peak on asialofetuin. 3. The use of small saccharidic acceptors (phenylgalactose, lactose, lacto-N-fucopentaose I) and the analysis of fucosylated asialoglycoproteins indicate that the first activity corresponds to an alpha-(3/4)-fucosyltransferase and the second one to an alpha-(1-2)-fucosyltransferase. 4. Protein analysis by polyacrylamide gel electrophoresis in the presence of SDS for each enzyme shows two bands corresponding to a mol. wt of about 65,000 and 70,000. The two enzymes have the same sensitivity to the action of N-ethylmaleimide.

Endogenous glycosyltransferases glucosylate lipids in flagella of Euglena

Flagella, intact deflagellated cells and isolated cell surfaces of the unicell , Euglena were separately assayed for glycosyltransferase activity by incubating these fractions with uridine diphosphate-[3H]glucose and isolating radiolabeled products. Most of the label was incorporated into lipophilic products, soluble in chloroform/methanol, which could be separated via thin layer chromatography or LH-60 chromatography into four distinct classes. The most polar of these products was extracted from flagella and purified by column chromatography for use as an in vitro substrate to identify flagella-associated glycosyltransferases. After flagella were treated with the detergent CHAPS , a soluble fraction was removed that was capable of glycosylation in solution. The glycosyltransferase(s) responsible for this activity were further enriched on sucrose or fructose gradients and ultimately identified on acrylamide gels through the combined use of nondenaturing gels, dial-[3H]uridine diphosphate binding, and fluorography. The enzyme had an apparent monomer molecular weight of 32,000 and consisted of four or fewer subunits. The occurrence of endogenous glycosyltransferase(s) in flagella suggests that modifications and/or assembly of the flagella surface can take place in situ in this organism.