Trichomonas vaginalis Cysteine Proteinases: Iron Response in Gene Expression and Proteolytic Activity

Figure 1

Processing involved in cysteine proteinase activation. (a) Representation of the interaction between substrate and the active sites of a cysteine proteinase. Subsites in the protease are denoted by “S” and subsites in the substrate by “P.” The active cysteine sulfhydryl nucleophile is represented as –SH and the scissile bond is shown. Processing of clan CA (b) and clan CD (c) cysteine proteinases; the signal peptide for cellular trafficking (light blue), the propeptide located in the N-terminus (dark blue) of the catalytic domain (green) in clan CA and in the C-terminus (red) of the catalytic domain (green) for clan CD. The catalytic residues C (Cys), H (His), and N (Asn) are indicated. Arrowheads show conserved Cys residues that can form disulfide bonds. Asterisks show N-glycosylation sites.