A developmentally regulated cysteine protease gene family in Haemonchus contortus

The nucleotide sequence of a gene encoding a 35-kDa thiol protease of the parasitic nematode Haemonchus contortus has been determined. The gene, designated AC-2, shares 97% nucleotide sequence identity and 98% amino acid identity with previously characterized AC-1 cDNAs encoding the thiol protease. The AC-2 gene spans 8 kb and appears to contain 11 introns, ranging in size from 57 bp to over 5.2 kb. One of the introns interrupts the proposed active site region that is conserved between the H. contortus protease and the related thiol proteases cathepsin B and papain. Southern blot hybridization experiments indicate that the protease is encoded by a small gene family in H. contortus. Rabbit antisera prepared against the recombinant protein react on Western blots with 35 and 37-kDa proteins of adult worms. These proteins were not detectable by Western blot analysis in three larval parasitic developmental stages of H. contortus. Northern blot hybridizations indicate that mRNA transcripts for the gene family are present at low levels in a mixed population of third- and fourth-stage larvae but highly abundant in adult worms. Expression of the protease correlates with blood-feeding and suggests a role for the protease in blood digestion.