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Conformations of Synthetic Model Peptides for Plasmodium falciparum Circumsporozoite Protein in Me2SO by 1H NMR and Distance Geometry Calculations

A series of terminally blocked peptides consisting of a tetrapeptide repeat, Boc-Asn-Ala-(Asn-Pro-Asn-Ala)n=0,1,2,5,17-Asn-Pro-OBzl, has been synthesized and one and two dimensional 1H NMR studies in dimethyl sulfoxide (Me2SO)-d6 as well as distance geometry calculations have been carried out. The repeating tetrapeptide units constitute the central area of the circumsporozoite coat protein of human malaria parasite Plasmodium falciparum. The two dimensional nuclear Overhauser effect (NOE) data observed in Me2SO and the information from the temperature dependence of the amide proton chemical shifts were used as constraints in distance geometry calculations. The result suggests that each -(Asn-Pro-Asn-Ala)- tetrapeptide forms a structural unit, a considerable population of which exists as unique turnlike structures.