Molecular and biochemical characterisation and recognition by the immune host of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) of the abomasal nematode parasite Teladorsagia circumcincta

- Full length cDNAs encoding GAPDH was cloned from T. circumcincta.
- TcciGAPDH (1023 bp) cDNA encoded 341 amino acid proteins.
- The predicted amino acid sequences showed 68-93% similarity to other helminth sequences.
- Antibodies from nematode-exposed sheep recognised the recombinant protein.

A 1023 bp full length cDNA encoding Teladorsagia circumcincta GAPDH (TeciGAPDH) was cloned, expressed in Escherichia coli and the recombinant protein purified and its kinetic properties determined. A phylogenetic tree was constructed using helminth GAPDH sequences. The predicted protein consisted of 341 amino acids and was present as a single band of about 38 kDa on SDS-PAGE. Multiple alignments of the protein sequence of TeciGAPDH with homologues from other helminths showed that the greatest similarity (93%) to the GAPDH of Haemonchus contortus and Dictyocaulus viviparus, 82-86% similarity to the other nematode sequences and 68-71% similarity to cestode and trematode enzymes. Substrate binding sites and conserved regions were identified and were completely conserved in other homologues. At 25 °C, the optimum pH for TeciGAPDH activity was pH 8, the Vmax was 1052 ± 23 nmol min−1 mg−1 protein and the apparent Km for the substrate glyceraldehyde-3-phosphate was 0.02 ± 0.01 mM (both mean ± SD, n = 2). Antibodies in both serum and saliva from field-immune, but not nematode-naïve, sheep recognised recombinant TeciGAPDH in enzyme-linked immunosorbent assays. The recognition of the recombinant protein by antibodies generated by exposure of sheep to native GAPDH indicates similar antigenicity of the two proteins.

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