Characterisation of potential vaccine targets in Haemonchus contortus

In a recent study, bioinformatics and RNA interference (RNAi) were used to look for the genes responsible for the acute lethal or developmental arrest in Haemonchus contortus. Out of the fifty-six H. contortus genes selected as potential targets, 41 provided strong to moderate phenotype. Seven genes were then selected for expression, purification and characterisation in the present study. A 981 bp full-length cDNA encoding H. contortus fatty acid synthase thioesterase domain (HcFAS-TE) was cloned, expressed in Escherichia coli, and the recombinant protein purified and biochemically characterised. The protein sequence of HcFAS-TE showed the greatest similarity with FAS-TE of Teladorsagia circumcincta and Ancylostoma caninum. The optimum substrate concentration for recombinant HcFAS-TE was 125 µM, whereas the addition of 150 µM Orlistat reduced the HcFAS-TE activity by 85 %. A 1563 bp full-length aspartyl tRNA synthetase (HcDRS-1), a 3048 bp full-length glutamyl tRNA synthetase (HcERS-2), a 1482 bp vacuolar ATPase subunit A (HcVHA-12), a 1362 bp transcriptional co-activator histone acetyltransferase domain (HcCBP-1) and a 1362 bp full-length serum glucocorticoid-inducible kinase (HcSGK-1) and a 1152 bp full-length NADH-dependent oxidoreductase (HcF36A2.3) were also cloned, expressed in E. coli and purified. Despite varying assay conditions, there were no detectable activities for HcDRS-1, HcERS-2 or HcF36A2.3. Due to the assay complexity, no attempts were made to assay HcSGK-1 or HcVHA-12. Antibodies in serum and saliva from field-immune, but not parasite-naïve, animals recognised recombinant HcFAS-TE, HcVHA-12, HcCBP-1, HcF36A2.3, HcDRS-1, and HcERS-2, but not HcSGK-1, showing that an immune host has developed a response against the proteins.