Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/1998
Publication Date: N/A
Interpretive Summary: Parasites and their hosts engage in a continuous struggle; the host attempting to rid itself of the parasite, while the parasite attempts to maintain itself within the host. Evolutionary pressures from host defense mechanisms and the biologically hostile environments in which parasites live may accelerate structural changes in parasite molecules to better modulate the effects of host defenses on the parasite. We have isolated 3 isoforms of an elastase inhibitor from Anisakis simplex. These isoforms are 95-98% identical at the amino acid level, with most of the variability restricted to the reactive site of the enzyme. This hypervariable region may have arisen through accelerated evolution as a result of selective pressures from host enzymes on parasite inhibitors. These studies will help to elucidate the mechanisms by which parasites adjust to environmental pressures, and may help in the selection of target molecules for control strategies based on rational drug design.
Technical Abstract: Three isoforms of a serine protease inhibitor were isolated from Anisakis simplex. RT-PCR was used to amplify total RNA isolated from third stage larvae. The first strand cDNA was used as a template to selectively amplify a partial cDNA for the inhibitors, which was sequenced, and this sequence was used to design internal primers to obtain the full length sequences of each of the isoforms. The three isoforms were 95-98% identical at the amin acid level, and code for a protein of 60 amino acids. A hypervariable region exists within the reactive site of the three isoforms, which accounts for most of the lack of complete identity. The high identity seen among these isoforms suggests that these parasite inhibitors may have undergone a mutational burst as a result of selective pressures from host enzymes.