| dc.description | Larvae of the parasitic nematode Pseudoterranova decipiens (commonly known as sealworm) infect several species of demersal fish in the North Atlantic, including Atlantic cod (Gadus morhua). The most important definitive hosts of the parasite appear to be grey seals (Halichoerus grypus). Immunological control of the P. decipiens population might be achieved by immunizing seals against the major antigens of the worm. Polyclonal sera raised in adult seals against P. decipiens indicated that there were two major antigens, of 40 kDa and 105 kDa. A cDNA clone of the 40 kDa antigen, encoding a unique 333 amino acid haemoglobin was isolated from the nematode. The predicted protein sequence contains an 18 amino acid hydrophobic signal sequence and has a calculated mass of 37.6 kDa in the mature form. The predicted protein sequence also reveals an internal duplication of a 154 amino acid domain (51% identity). Both domains have significant sequence homology to other haemoglobins, in agreement with a duplication event. The nematode globin gene has a unique six-intron, seven-exon structure that contains an intron in a position previously thought to be unique to plants. The nematode globin also contains a unique intron, absent in other extracellular invertebrate globin genes, between its secretory peptide leader sequence and its coding sequence. The variation in colour of the larval nematodes from reddish-brown to white is due to variations in the concentration of haemoglobin in the pseudocoelomic fluid. While reddish brown worms contain more haemoglobin, this variation is not due to greater quantities of globin mRNA. Thus the level of haemoglobin may be controlled at the post-transcriptional level. The full length cDNA clone and fragments encoding the first and second repeats of this protein were expressed in bacteria to produce sufficient quantities of protein for vaccines. | en_US |
