THE SURFACE TRANS-SIALIDASE FAMILY OF TRYPANOSOMA-CRUZI

Trypanosomes cannot synthesize sialic acids. Infectious stages of the life cycle of the human pathogen Trypanosoma cruzi express a cell-surface glycolipid-anchored trans-sialidase, which can transfer sialic acid between glycoconjugates. Sialic acid is transferred from host cell-surface and serum sialylglycoproteins to trypanosome cell-surface glycoconjugates. The transfer reaction is specific for donors with terminal alpha-2,3-linked sialic acid, and terminal beta-1,4-linked galactose is the preferred acceptor. In the absence of an acceptor, the enzyme acts as a hydrolase, but cleavage is less efficient than transfer. Trans-sialidase activity is attributable to a few members of a large family of T. cruzi surface glycoproteins, many of which are simultaneously expressed. The functions of the trans-sialidase surface glycoprotein family are unknown but may be important for adhesion, invasion, virulence, or pathogenicity. A trans-sialidase is also expressed in the procyclic forms of Trypanosoma brucei.