Evolutionary diversity of social amoebae N-glycomes may support interspecific autonomy

Multiple species of cellular slime mold (CSM) amoebae share overlapping subterranean environments near the soil surface. Despite similar life-styles, individual species form independent starvation-induced fruiting bodies whose spores can renew the life cycle. N-glycans associated with the cell surface glycocalyx have been predicted to contribute to interspecific avoidance, resistance to pathogens, and prey preference. N-glycans from five CSM species that diverged 300-600 million years ago and whose genomes have been sequenced were fractionated into neutral and acidic pools and profiled by MALDI-TOF-MS. Glycan structure models were refined using linkage specific antibodies, exoglycosidase digestions, MALDI-MS/MS, and chromatographic studies. Amoebae of the type species Dictyostelium discoideum express modestly trimmed high mannose N-glycans variably modified with core α3-linked Fuc and peripherally decorated with 0-2 residues each of β-GlcNAc, Fuc, methylphosphate and/or sulfate, as reported previously. Comparative analyses of D. purpureum, D. fasciculatum, Polysphondylium pallidum, and Actyostelium subglobosum revealed that each displays a distinctive spectrum of high-mannose species with quantitative variations in the extent of these modifications, and qualitative differences including retention of Glc, mannose methylation, and absence of a peripheral GlcNAc, fucosylation, or sulfation. Starvation-induced development modifies the pattern in all species but, except for universally observed increased mannose-trimming, the N-glycans do not converge to a common profile. Correlations with glycogene repertoires will enable future reverse genetic studies to eliminate N-glycomic differences to test their functions in interspecific relations and pathogen evasion.