CONICET | Buscador de Institutos y Recursos Humanos

Tandemly repetitive polyproteins (TRPs) are rare in nature. They are produced as large precursor polypeptides, comprising repeated units of similar or identical amino acid sequence that are post-translationally cleaved into a dozen or so copies of functionally similar proteins. The polyprotein allergens/antigens of nematodes (NPAs) belong to this family, are small, helix-rich proteins, and have no known structural counterparts in other phyla. The NPAs present in Ascaris suum (ABA) are cleaved posttranslationally into multiple ~15 kDa protein subunits which may have similar or different functions. It is important to note that they also represent a novel class of lipid binding proteins from helminths group. ABA-1A, a single subunit of this family of proteins, is found in high amounts both in the pseudocelomic fluid of adult worms and in the excretion/secretion products from all parasitic stages. Recently, the structure of ABA-1A has been solved showing two binding sites with different characteristics. The protein adopts a novel seven-helical fold comprising a long central helix that participates in two hollow four-helical bundles on either side (Meenan et al., 2011 doi:10.1371/journal.pntd.0001040). Although structural and functional characterisation has been performed on the single subunit, ABA-1A, there are no reports on the polyprotein array. In this project we aim at getting further insight into the unusual translation process of these proteins. To this end we designed, constructed and expressed a tandem protein composed of two ABA-1A subunits. Preliminary analysis using spectroscopic techniques (fluorescence and CD) have shown that there are no differences in the secondary and tertiary structure between the tandem protein and the ABA-1A subunit alone. These results would suggest that there are almost no interactions between subunits during polypeptide folding in vivo when it is being synthesized.