The ABA-1 protein of Ascaris lumbricoides (of humans) and Ascaris suum (of pigs) is abundant in the pseudocoelomic fluid
of the parasites and also appears to be released by the tissue-parasitic larvae and the adult stages. The genes encoding the
polyprotein precursor of ABA-1 (aba-1) were found to be arranged similarly in the two taxa, comprising tandemly
repeating units encoding a large polyprotein which is cleaved to yield polypeptides of approximately 15 kDa which fall
into 2 distinct classes, types A and B. The polyprotein possibly comprises only 10 units. The aba-1 gene of A. lumbricoides
is polymorphic, and the majority of substitutions observed occur in or near predicted loop regions in the encoded proteins.
mRNA for ABA-1 is present in infective larvae within the egg, and in all parasitic stages, but was not detectable in
unembryonated eggs. ABA-1 mRNA was confined to the gut of adult parasites, and not in body wall or reproductive
tissues. Recombinant protein representing a single A-type unit for the A. lumbricoides aba-1 gene was produced and found
to bind retinol (Vitamin A) and a range of fatty acids, including the pharmacologically active lipids lysophosphatidic acid,
lysoplatelet activating factor, and there was also evidence of binding to leukotrienes. It failed to bind to any of the
anthelmintics screened. Differential Scanning Calorimetry showed that the recombinant protein was highly stable, and
unfolded in a single transition at 90·4 °C. Analysis of the transition indicated that the protein occurs as a dimer and that
the dimer dissociates simultaneously with the unfolding of the monomer units.