RESUMO
The biosynthesis of glycoprotein N-linked oligosaccharides in D. discoideum is initiated by the transfer of a large precursor glycan from a carrier lipid. The subsequent processing of this precursor is dramatically dependent upon the stage of development. In early development processing retains the high mannose structure of the precursor and modifies some glycans by addition of fucose to core sugars and sulfate and phosphate to others. These reactions are coordinately lost during aggregation. Processing in late development extensively trims the precursor and adds fucose to peripheral mannose units of the smallest glycans. These reactions appear coincident with formation of tips on cell mounds. Experiments in which cells were starved in shaken suspension suggest that intercellular contacts and cyclic AMP signals may be sufficient to cause the controlled expression of these two alternate sets of processing enzymes.
