| Malaria is the most prevalent parasitic human disease. It claims the lives of more children worldwide than any other infectious disease. The use of synthetic peptides for immunization against malaria is a very attractive strategy for antigen delivery, since they are relatively easy to obtain in large quantities with high purity. Peptides that correspond to the epitope region of the circumsporozoite protein (CSP) of Plasmodium falciparum have been extensively studied to understand their immunogenicity. Amongst these peptides, a multi-antigenic peptide construct, T1BT*; containing the T1, B-cell activating epitopes (NANP)3, and the universal T* epitope; has been shown to elicit antisporozoite antibodies and gamma interferon-screening T-cell responses. Nuclear Magnetic Resonance (NMR) spectroscopy and molecular dynamics calculations (MD) were used to determine the solution structures of this peptide and its analogue, T1B'T*, where the B-cell activating tandem repeat was modified to be B' = (NPNA)3. These structures were compared to determine the main differences and similarities between these peptides. It was found that there are radical different between their structures, with the T1B'T* showing strong helical tendencies. NMR, together with MD, provided information about the topologies of T1BT* and T1B'T*. This information could be used to correlate structure and antiplasmodial activity for these peptides. It was shown that calcium influences the development of several stages of the P. falciparum parasite. However there is very little knowledge regarding calcium coordination to CSPs. With this idea in mind, another CSP peptide, (NANPNVDP)3NANP, was also studied through NMR and MD to determine its potential calcium-chelation properties through the D amino acids. The results of our investigation strongly support Ca2+ coordination by the peptide under study through the shifts of the signals for the protons in the D and V22 amino acids. This peptide has the same amino acid sequence as the repeat region of CSP adjacent to region I. It is therefore possible that the CSP of P. falciparum can chelate Ca2+ ions even more efficiently, since it contains four NVDP blocks to produce a tetrahedral Ca2+ center. NMR spectroscopy was also used to determine the relative concentration of NAs and their anions in the aqueous phase of water-crude oil systems. Naphthenic acids (NAs) are found in different concentrations in crude oils worldwide and are being recognized as potential emulsion stabilizers. 1H-NMR was used to understand the impact of the aqueous phase ionic strength on the partitioning of the naphthenic acids between water and crude oils. Our results show that higher ionic strength is, in general, conducive to higher rate of partitioning of the naphthenic acids. Higher concentration of organic components is found in the brine with higher ionic strength. The results of this investigation allowed us to propose that the lower stability of the water-in-crude oil emulsions at higher ionic strength of the aqueous phase during early aging time might result from the higher concentration of naphthenic components in the brine. |
