THIOREDOXIN PEROXIDASE FROM ONCHOCERCA-VOLVULUS - A MAJOR HYDROGEN-PEROXIDE DETOXIFYING ENZYME IN FILARIAL PARASITES

Random screening of an Onchocerca volvulus third-stage (L3) cDNA libra ry identified a highly abundant cDNA encoding a newly discovered antio xidant enzyme, thioredoxin peroxidase (TPx), a member of the peroxidox in superfamily. This TPx cDNA (Ov-tpx-2) encodes a polypeptide of 199 amino acid residues with a calculated molecular weight of 21 890 Da. T he Ov-tpx-2 cDNA represents roughly 2.5% of the total cDNAs from the L 3 cDNA library. The gene was expressed in Escherichia coil and the pro tein product was shown to have antioxidant activity. Antiserum raised against Ov-TPX-2 recognized a native protein from extracts of both the L3 and adult-stages with a molecular weight of 22 kD. The localizatio n and stage-specificity of Ov-TPX-2 protein was analyzed by immunocyto chemistry and immunoelectron microscopy using monospecific antibodies. Expression was detected in late first stage larvae during development in the vector and increased in intensity during differentiation to th e infective L3-stage. The antigen was also detected in post-infective larvae and adult worms. In larvae, Ov-TPX-2 protein was predominantly localized to the hypodermis and cuticle, with additional sites in the hypodermal chords and multivesicular bodies. In adult worms, the prima ry sites of expression were the uterine epithelium and intestine, with additional labeling of the body wall and cuticle. Developing embryos and microfilariae in utero were bathed in Ov-TPX-2 protein discharged from epithelial cells. These results suggest that Ov-TPX-2 may protect the parasites from being damaged by host-generated oxidative stress a nd that Ov-TPX-2 protein provides the H2O2-detoxifying activity predic ted but not previously identified in filarial parasites. Its highly up regulated expression in infective larvae may aid in parasite establish ment following transmission to the definitive host. (C) 1998 Elsevier Science B.V. All rights reserved.