A NOVEL TYPE OF GLUTATHIONE-S-TRANSFERASE IN ONCHOCERCA-VOLVULUS

Onchocerca volvulus is a pathogenic human filarial parasite which, lik e other helminth parasites, is capable of evading the host's immune re sponses by a variety of defense mechanisms which are likely to include the detoxification and repair mechanisms of the enzyme glutathione S- transferase (GST). In this study, we show that one of the previously d escribed GSTs from O. volvulus appears to possess the characteristics of a secreted enzyme. When the complete O. volvulus GST1 (OvGST1) sequ ence presented here is compared with those of other GSTs, 50 additiona l residues at the N terminus are observed, the first 25 showing charac teristics of a signal peptide. This is consistent with the N-terminal sequence data on the native mature enzyme which begins at amino acid 2 6, based on the deduced protein sequence from the cDNA. The native pro tein, without the signal peptide sequence, possesses a 24-amino-acid e xtension not present in other GSTs. The deduced amino acid sequence of the OvGST1 cDNA clone,vas shown to possess four potential N-glycosyla tion sites. Digestion of O. volvulus homogenate with endoglycosidase, followed by detection of OvGST1 with specific antibody, indicated that the enzyme possesses at least two N-linked oligosaccharide chains. Ge l filtration of the Escherichia coli-produced recombinant OvGST1 showe d that it is enzymatically active as a nonglycosylated dimer. OvGST1 i s found in the media surrounding adult worms maintained ih culture, in dicating that, in vitro, this enzyme is released from the worm. The st rongest immunostaining fdr OvGST1 was observed in the outer cellular c overing of the adult worm body, the syncytial hypodermis, especially i n the interchordal hypodermis, where the peripheral membrane forms a s eries of lamellae which run into the outer zone of the hypodermal cyto plasm.