Cloning and characterization of glutamate dehydrogenase (GDH) from the gutof Haemonchus contortus

Vaccination of lambs with the membrane-bound (S3) thiol-Sepharose binding p rotein (TSBP) fraction derived from the gut of Haemonchus contortus confers significant protection against homologous challenge. The S3 TSBP peptide p rofile is dominated by a major protein of ca. 60 kDa which is strongly reco gnized by antisera from sheep demonstrably protected following immunization with S3 TSBP. In an attempt to identify this protein, sera from protected lambs were employed to screen a lambda gt11 cDNA library of the adult paras ite and resulted in the isolation of numerous clones encoding a homologue o f the mitochondrial enzyme, glutamate dehydrogenase (GDH). GDH enzyme activ ity was readily demonstrable in S3 TSBP material and immunolocalization stu dies showed that the enzyme was localized to the cytoplasm of the parasite' s gut. Furthermore, the enzyme appeared to be developmentally regulated, wi th both GDH mRNA and protein expressed almost exclusively during the blood- feeding parasitic stages.