Trypanosoma brucei gambiense and T. b. rhodesiense: Concanavalin A Binding to the Membrane and Flagellar Pocket of Bloodstream and Procyclic Forms1

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Abstract
We have measured binding of fluorescein‐conjugated succinyl‐concanavalin A (Fl‐s‐Con A) to bloodstream and procyclic forms of Trypanosoma brucei gambiense and to bloodstream forms of T. b. rhodesiense by flow cytofluorimetry. Bloodstream forms bound an order of magnitude less lectin than procyclic forms. Trypsin‐treating cells enhanced binding of Fl‐s‐Con A to bloodstream forms 3–16‐fold depending on the strain and the length of trypsinization but had little effect on Fl‐s‐Con A binding by procyclics. The trypsinization protocol used did not remove major common glycoproteins detected on lectin blots of either life cycle form but removed >95% of the variant specific glycoprotein and fragments derived from this protein of bloodstream forms. Microscopically detectable Fl‐s‐Con A binding to bloodstream forms was confined to the flagellar pocket. Trypsinized bloodstream forms and procyclics bound Fl‐s‐Con A in the flagellar pocket, on the flagellum, and on the cell surface. Lectin remained cell associated but appeared to redistribute towards the flagellum and pocket when cells that had bound lectin on ice were subsequently incubated at physiological temperatures. The Fl‐s‐Con A binding had specificity characteristic of the interaction between the lectin and oligosaccharides. These results are consistent with the hypothesis that the variant specific surface glycoprotein blocks binding of the lectin to surface glycoproteins of bloodstream forms and suggest that concanavalin A‐binding glycoproteins are abundant in the flagellar pocket of both life cycle forms.