SA85-1 proteins of Trypanosoma cruzi lack sialidase activity

Trypanosoma cruzi infects a wide range of mammalian species, and replicates within many different cell types [1]. Numerous reports indicate that trypomastigote surface proteins facilitate adhesion and invasion of mammalian cells [1]. Recently, several genes that are expressed specifically by mammalianstage parasites have been shown to encode surface proteins with homology to sialidases [2]. Two of these, genes have been shown to encode functional sialidases when expressed in Escherichia coli [3,4]. Other proteins, with homology to sialidase, apparently lack intrinsic sialidase activity, and their function remains unclear [4]. In addition, sialidase and trans-sialidase activities appear to be catalyzed by the same protein, and to represent coupled steps of the same reaction; the former representing sialic acid transfer to water, and the latter transfer to another carbohydrate [4]. We have described the SA85-1 family of surface proteins expressed by mammalianstage parasites that have homology to sialidases [5,6]. Hybridization to a cDNA named 1.1 (cl.1), or reactivity to antibodies purified with a recombinant protein generated by expression of cl. 1 (anti-cl. 1 antibodies) define