Gene structure of the extracellular glutathione S-transferase from Onchocerca volvulus and its overexpression and promoter analysis in transgenic Caenorhabditis elegans

Two highly similar genes encoding unique extracellular, glycosylated glutathione S-transferases (GSTs) of the human-pathogenic nematode, Onchocerca volvulus (Ov-GST1a and Ov-GST1b), have been isolated and characterised, The genes are approximate to 3 kb in length and consist of seven exons interrupted by introns of approximate to 100 bp in length, with the exception of intron II, which is approximate to 1.6 kb in length. Interestingly, exon I and II encode a signal peptide and an N-terminal extension before sequence homology to other GSTs begins. The 5' flanking region was sequenced and analysed for transcription factor binding sites. Consistent with the lack of a TATA box. analysis of the mRNAs by primer extension showed multiple transcription start sites spread over a 60 bp region. To examine the activity and specificity of the Ov-GST1a gene promoter, we have exploited Caenorhabditis elegans as a heterologous transformation system. To analyse whether transgenic C. elegans are able to carry out processing and post-transcriptional modifications of the Ov-GST1a correctly. the protein was ectopically overexpressed in C. elegans. The parasite-derived Ov-GST1a gene product was correctly processed in transgenic C. elegans and posttranslational modifications., such as signal peptide cleavage and N-glycosylation, were performed successfully. This further demonstrates the potential of C. elegans as a host for expression of candidate vaccine antigens from O. volvulus and affirms the role of C. elegans as a model for parasitic nematodes. (C) 2001 Elsevier Science B.V. All rights reserved.