Highly purified lectins with specificities for receptor molecules containing sialic acid, N-acetylglucosamine (DGlcNAc), N-acetylgalactosamine (D-GalNAc), galactose (D-Gal), mannose-like residues (D-Man) or L-fucose (LFuc), were used to determine changes in cell-surface carbohydrates of the protozoal parasite Trypanosomu cruzi during metacyclogenesis under chemically defined conditions. Of the D-GalNAc-binding lectins, BS-I selectively agglutinated metacyclic trypomastigotes, MPL was selective for replicating epimastigotes, whereas SBA strongly agglutinated all developmental stages of T. cruzi. WGA (sialic acid and/or D-GIcNAc specific) was also reactive with differentiating epimastigotes and metacyclic trypomastigotes but displayed a higher reactivity with replicating epimastigote forms. A progressive decrease in agglutinating activity was observed for jacaline (specific for D-Gal) during the metacyclogenesis process; conversely, a progressive increase in affinity was observed for RCA-I (D-Gabspecific), although the reactivity of other D-Gal-specific lectins (PNA and AxP) was strong at all developmental stages. All developmental stages of T. cruzi were agglutinated by Con A and Lens cufinaris lectins (specific for D-Man-like residues); however, they were unreactive with the L-fucose-binding lectins from Lotus tetrugonolobos and Ufex europueus. These agglutination assays were further confirmed by binding studies using I z51-labelled lectins. Neuraminidase activity was detected in supernatants of cell-free differentiation medium using the PNA hemagglutination test with human A erythrocytes. The most pronounced differences in lectin agglutination activity were observed between replicating and differentiating epimastigotes, suggesting that changes in the composition of accessible cell-surface carbohydrates precede the morphological transformation of epimastigotes into metacyclic trypomastigotes.

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ABSTRACT. Cell surface carbohydrates of three phytoflagellates, Phytomonas francai. Phytomonas serpens and Phytomonas sp. from different hosts including cassava, coreid insect Phthia picta and the milkweed plant Euphorbia hyssopifolia, respectively, were analysed by agglutination assays employing a battery of highly purified lectins with affinity for receptor molecules containing N‐acetylglucosamine (d‐GlcNAc), N‐acetylgalactosamine (D‐GalNAc), galactose, mannose‐like (D‐Man‐like) residues and fucose, and by binding assay using radiolabeled [125I]‐wheat germ agglutinin (WGA) and fluorescent WGA lectin, as well as glycosidases of known sugar specificity, Escherichia coli K with mannose‐affinity fimbrial lectin was also used as an agglutination probe. In general, the presence of D‐GlcNAc. D‐GalNAc and D‐Man‐like residues was detected in the phytomonads' plasma membrane. These sugar moieties were confirmed in whole cell hydrolysates as assessed by gas‐liquid chromatography (GLC) which in addition, also showed the presence of galactose and xylose. However, marked differences in cell surface carbohydrate structures were observed. Wheat germ agglutinin, which binds to sialic acid and/or d‐GlcNAc‐containing residues, shows selective agglutinin activities for P. francai and Phytomonas sp., while Bandeiraea simplicifolia II agglutinin (which recognizes d‐GlcNAc units) specifically bound to Phytomonas sp. Helix pomatia agglutinin which binds to D‐GalNAc‐containing residues reacted preferentially with Phytomonas sp. and P. serpens. Con A, which recognizes D‐Man‐like receptors, agglutinates all the phytomonads; however, the higher interaction was observed with Phytomonas sp. P. francai was selectively agglutinated in the presence of E. coli fimbrial lectin. Fluorescence WGA binding was significantly decreased by N‐acetylglucosaminidase activities and the cell agglutination was not altered by neuraminidase treatment, suggesting the presence of an exposed D‐GlcNAc moiety on the P. francai and Phytomonas sp. surfaces. Binding studies with [125I]‐WGA essentially confirmed the fluorescence WGA binding and agglutination assays.

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Wild type Crithidia fasciculata and three drug‐resistant mutant strains that have shown “flagellar adherence” were studied as to their ability to agglutinate with lectins specific for receptor molecules containing N‐acetyl glucosamine, N‐acetyl galactosamine, galactose, mannose‐like residues, fucose, and sialic acid. Escherichia coli with mannose‐sensitive fimbriae was also used as an agglutination probe. The presence of D‐GalNAc, D‐Gal, and mannose‐like residues was detected in the wild strain. Generally, in the mutants, residues of these sugar units were present in greater concentrations when compared to the wild type strain. β‐Galactosidase treatment showed that β‐D‐Galp units are exposed on the cell membrane. All types of cell agglutination including flagellum‐flagellum (F‐F), flagellum‐soma (F‐S), and soma‐soma (S‐S) were observed when lectins were used; however, with E. coli only the F‐F type of cell agglutination was observed with the wild type strain and the TFRR1 mutant. All types of agglutination were observed with the other two mutants.

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