Distribution of developmentally regulated trans-sialidases in the Kinetoplastida and characterization of a shed trans-sialidase activity from procyclic Trypanosoma congolense.

The expression of developmentally regulated sialidase and trans-sialidase activities in kinetoplastid protozoa was investigated. The occurrence of these enzymes was found not to be a common feature among the Kinetoplastida, but to be restricted to distinct developmental life cycle stages of only a few species. While sialidases without trans-sialylating activities were demonstrated in Trypanosoma vivax and T. rangeli, trans-sialidase activity is expressed throughout the brucei-group and in T. congolense. Neither T. evansi, nor T. equiperdum express sialidases or trans-sialidases. Furthermore, the absence of both, sialidase and trans-sialidase activities was proven in the Leishmania, Crithidia, Herpetomonas, Leptomonas and Phytomonas, respectively. In all species tested, the occurrence of sialic acids coincides with the expression of trans-sialidase activity. Those parasites, which lack trans-sialidases or only display regular sialidases, also lack cell-bound sialic acids. The regular sialidase activity from bloodstream form T. vivax was characterized. The trans-sialidase from T. congolense is restricted to the procyclic culture forms and is shed into the culture medium. The enzyme has a pH-optimum at pH 7.0, displays sensitivity towards chlorides and is resistant against commonly used sialidase inhibitors. T. congolense trans-sialidase transfers preferentially alpha(2-3)-linked sialic acids onto terminal beta-galactose residues. Also hydroxylated sialic acids (Neu5Gc) are transferred. The major glycoprotein GARP from procyclic T. congolense was identified as one potential natural sialic acid acceptor on the parasite's surface. In order to facilitate the characterization of trans-sialidases a novel, fluorimetric trans-sialidase assay was developed.