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-surf ace glycolipid-anchored trans-sialidase, which can transfer sialic aci d between glycoconjugates. Sialic acid is transferred from host cell-s urface and serum sialylglycoproteins to trypanosome cell-surface glyco conjugates. 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 a cts as a hydrolase, but cleavage is less efficient than transfer. Tran s-sialidase activity is attributable to a few members of a large famil y of T. cruzi surface glycoproteins, many of which are simultaneously expressed. The functions of the trans-sialidase surface glycoprotein f amily are unknown but may be important for adhesion, invasion, virulen ce, or pathogenicity. A trans-sialidase is also expressed in the procy clic forms of Trypanosoma brucei.