Recombinant and native TviCATL from Trypanosoma vivax: Enzymatic characterisation and evaluation as a diagnostic target for animal African trypanosomosis

African animal trypanosomosis (nagana) is caused by tsetse-transmitted protozoan parasites. Their cysteine proteases are potential chemotherapeutic and diagnostic targets. The N-glycosylated catalytic domain of Trypanosoma vivax cathepsin L-like cysteine protease, rTviCATL _cat , was recombinantly expressed and purified from culture supernatants while native TviCATL was purified from T. vivax Y486 parasite lysates. Typical of Clan CA, family C ₁ proteases, TviCATL activity is sensitive to E-64 and cystatin and substrate specificity is defined by the S ₂ pocket. Leucine was preferred in P ₂ and basic and non-bulky, hydrophobic residues accepted in P ₁ and P ₃ respectively. Reversible aldehyde inhibitors, antipain, chymostatin and leupeptin, with Arg in P ₁ and irreversible peptidyl chloromethylketone inhibitors with hydrophobic residues in P ₂ inhibited TviCATL activity. TviCATL digested host proteins: bovine haemoglobin, serum albumin, fibrinogen and denatured collagen (gelatine) over a wide pH range, including neutral to slightly acidic pH. The recombinant catalytic domain of TviCATL showed promise as a diagnostic target for detecting T. vivax infection in cattle in an indirect antibody detection ELISA.