Localisation of glycoproteins containing type 3 O-linked glycosylation to multilamellar bodies in Dictyostelium discoideum

Glycosylation of proteins in Dictyostelium discoideum has been recently classified into several types based on structural and mutational studies. Type 3 O-linked glycosylation contains fucose and N-acetyl-glucosamine and is recognised by the carbohydrate-specific monoclonal antibody MUD 62. The developmentally regulated cysteine proteinase, ddCP38B, is the major protein recognised by both MUD 62 and a second carbohydrate-specific monoclonal antibody, MUD 166, in vegetative cells using bacteria as a food source. Using immunofluorescence and immunogold labelling, glycoproteins carrying the MUD 62 and MUD 166-specific epitopes have been localised intracellularly to the lysosomal network and multilamellar bodies of D. discoideum. These bodies contain remnants of undigested bacteria and are egested from the cell prior to starvation-induced aggregation. These results suggest that extracellular glycoproteins carrying the Type 3 O-linkage, such as ddCP38B, may not be secreted via the conventional pathway but may be released into the medium following targeting to the multilamellar bodies.