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-sialid ase activities in kinetoplastid protozoa was investigated. The occurre nce of these enzymes was found not to be a common feature among the Ki netoplastida, but to be restricted to distinct developmental life cycl e stages of only a few species. While sialidases without trans-sialyla ting 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 sialid ases 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 specie s tested, the occurrence of sialic acids coincides with the expression of trans-sialidase activity. Those parasites, which lack trans-sialid ases or only display regular sialidases, also lack cell-bound sialic a cids. The regular sialidase activity from bloodstream form T. vivax wa s characterized. The trans-sialidase from T. congolense is restricted to the procyclic culture forms and is shed into the culture medium. Th e enzyme has a pH-optimum at pH 7.0, displays sensitivity towards chlo rides 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 fro m procyclic T. congolense was identified as one potential natural sial ic acid acceptor on the parasite's surface. In order to facilitate the characterization of trans-sialidases a novel, fluorimetric trans-sial idase assay was developed.