Biosynthesis of 117 antigen: A cell cohesion molecule in Dictyostelium discoideum

Abstract

117 antigen is involved in the process of intercellular cohesion in Dictyostelium discoideum [Brodie et al., 1983]. The antigen, a 69- and 72-kDa doublet, was found to arise from a 60- and 62-kDa precursor. The mature antigen contains N-linked oligosaccharides that are sulfated and fucosylated [Sadeghi et al., 1987]. These oligosaccharide chains are resistant to endoglycosidase H digestion. 117 antigen also contains a post-translationally added carbohydrate-containing modification(s). Unlike the N-linked oligosaccharide, this carbohydrate moiety is sensitive to periodate oxidation. 117 antigen is developmentally regulated, and the changes in rate of 117 antigen synthesis reflect changes in the cellular levels of its mRNA. 117 mRNA accumulates in starving cells and reaches its maximum when cells become aggregation competent. The mRNA levels then decline, and by the time the slug structure is formed, no 117 mRNA is present. 117 mRNA reaccumulates for a brief period during early culmination and then returns to an undetectable level.

Inhibition of N-linked glycosylation in Dictyostetium discoideum: Effects of aggregate formation

“…As shown, such cells possessed the 69-to 72-k Da bands characteristic of the mature antigen. We have previously shown that the broad band spanning this region is composed of a doublet [16]. Lane 2 contains the extract from cells which had been starved in the presence of 0.5 Fg/ml tunicamycin.…”

“…For immunoprecipitation, 10' cells were solubilized at a concentration of 5 x lo7 cell/ml in 50 mM Tris, pH 7.4, 150 mM NaC1, 5 mM EDTA containing 0.5% NP-40. The 117 antigen was immunoprecipitated using 117 monoclonal antibody and analyzed by SDS-PAGE as previously described [16]. To determine total protein synthesis or N-linked glycosylation, cells were labeled with either 1 pCi/ml [35S]-methionine or 10 pCi/ml [3H]mannose (or ['4C]-Nacetylglucosamine).…”

Evidence that a glycolipid tail anchors antigen 117 to the plasma membrane of Dictyostelium discoideum cells.

“…All of the oligosaccharide chains present on the precursor are sensitive to endoglycosidase H digestion, and the product of such digestion is a single polypeptide of 52 kDa (7). A subsequent posttranslational addition of a carbohydrate-containing structure(s) to both forms of the precursor accounts for the increase in molecular mass to produce the mature forms (7,8). This post-translational modification can occur independently of N-linked glycosylation (8).…”