Successful demonstration of an elusive cell coat in amebae

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.

Glycopeptidome of a heavily N-glycosylated cell surface glycoprotein of Dictyostelium implicated in cell adhesion

Genetic analysis has implicated the cell surface glycoprotein gp130 in cell interactions of the social amoeba Dictyostelium, and information about the utilization of the 18 N-glycosylation sequons present in gp130 is needed to identify critical molecular determinants of its activity. Various glycomics strategies, including mass spectrometry of native and derivatized glycans, monosaccharide analysis, exoglycosidase digestion, and antibody binding, were applied to characterize a nonanchored version secreted from Dictyostelium. s-gp130 is modified by a predominant Man(8)GlcNAc(4) species containing bisecting and intersecting GlcNAc residues and additional high-mannose N-glycans substituted with sulfate, methyl-phosphate, and/or core alpha 3-fucose. Site mapping confirmed the occupancy of 15 sequons, some variably, and glycopeptide analysis confirmed 14 sites and revealed extensive heterogeneity at most sites. Glycopeptide glycoforms ranged from Man(6) to Man(9), GlcNAc(0-2) (peripheral), Fuc(0-2) (including core alpha 3 and peripheral), (SO(4))(0-1), and (MePO(4))(0-1), which represented elements of virtually the entire known cellular N-glycome as inferred from prior metabolic labeling and mass spectrometry studies. gp130, and a family of 14 related predicted glycoproteins whose polypeptide sequences are rapidly diverging in the Dictyostelium lineage, may contribute a functionally important shroud of high-mannose N-glycans at the interface of the amoebae with each other, their predators and prey, and the soil environment.

Visual characterization of the extracellular matrix of Cochliobolus heterostrophus and a mutant strain with a modified matrix

Two layers of extracellular matrix (ECM) and a film secreted outside the layers were visualized on germlings of Cochliobolus heterostrophus Drechsler grown on glass slides, cellophane membranes, and the surface of maize leaves. A mutant of C. heterostrophus, less virulent than the wild type, possessed the inner layer of ECM and the film, but not the outer layer. Using cytochemical and morphological methods, we explored the hypothesis that the reduced virulence of the mutant in leaves was due to the absence of the outer layer of the ECM. All ECMs were characterized using ruthenium red fixation, cryopreservation, immunocytochemistry, and colloidal gold labeling, before being examined with light and electron microscopy. With immunocytochemistry, antigens were localized in islands stained with ruthenium red within the scaffolding of the outer layer of the wild-type ECM on leaf surfaces and within the leaf. In the mutant, antigens were localized in the film on leaf surfaces. Comparisons between leaves infected by the two strains showed hyphae to be enclosed within material interpreted to be host response within intercellular spaces of leaves infected by the mutant, but not the wild type.Key words: Cochliobolus, cytochemistry, extracellular matrix, microscopy, mutant, virulence.

Antibodies specific for gp40 inhibit cell-cell adhesion by cross-linking the protein on the surface of Dictyostelium purpureum

We have previously suggested a role for gp40 in cell-cell adhesion in Dictyostelium purpureum from the fact that antibodies specific for this protein inhibited adhesion in an in vitro assay [Springer: Dev Biol 133:447-455, 1989]. To further confirm the role mutants lacking the protein were isolated and characterized. To our surprise, the mutants had normal adhesive properties both in vitro and in situ. These results lead us to the conclusion that gp40 is not necessary for the cell-cell adhesions observed and may not be a molecule which directly participates in these adhesions. When studied further, we found that adhesion-inhibitory antibodies were only effective as divalent IgG. Monovalent Fab fragments of the same antibodies could not inhibit adhesion. The inhibitory antibodies also caused the cells to remain rounded and incapable of attaching to plastic surfaces. We conclude that when divalent antibodies specific for gp40 cross-link this protein on the cell surface a cytoskeletal change prevents them from attaching to substratum as well as to other cells, thereby inhibiting cell-cell adhesion. We suggest that an alternative mechanism for inhibition of cell-cell adhesion by divalent antibodies exists and should be considered before proposing a direct role for a protein in adhesion.

Mutants of Acanthamoeba castellanii resistant to erythromycin, chloramphenicol, and oligomycin

Cell lines of Acanthamoeba castellanii resistant to erythromycin (EryR), chloramphenicol (CapR), and oligomycin (OliR) have been isolated. These may be the first such mutants for A. castellanii. These mutants have been phenotypically stable for 2 years, surviving storage and vegetative multiplication in the absence of drugs. Resistance was specific for each drug, but double mutants (e.g. EryRCapR) were obtained by stepwise selection. Mutant frequencies were determined in multiwell plates; less than 10 colony forming units (CFU/10(5) amebas were observed in wild-type populations 12 days after incubation in 500 microgram Ery/ml, 2.5 mg Cap/ml, or 15 microgram Oli/ml. After 30 days, averages of 100 CFU/10(5) amebas were observed in Ery and Cap, whereas, frequencies for Oli remained unchanged. Frequencies for EryR and CapR were consistent with rates of recovery from these drugs in batch cultures. We were unable to obtain spontaneous mutants resistant to cycloheximide, emetine, 5-fluorodeoxyuridine, or ethidium bromide. EryR, CapR and OliR could be mitochondria mutants.