CONFORMATIONS OF SYNTHETIC MODEL PEPTIDES FOR PLASMODIUM-FALCIPARUM CIRCUMSPOROZOITE PROTEIN IN ME(2)SO BY H-1-NMR AND DISTANCE GEOMETRY CALCULATIONS

A series of terminally blocked peptides consisting of a tetrapeptide r epeat, Boc-Asn-Ala-(Asn-Pro-Asn-Ala)(n = 0,1,2,5,17)-Asn-Pro-OBzl, has been synthesized and one and two dimensional H-1 NMR studies in dimet hyl sulfoxide (Me(2)SO)-d(6) as well as distance geometry calculations have been carried out. The repeating tetrapeptide units constitute th e central area of the circumsporozoite coat protein of human malaria p arasite Plasmodium falciparum. The two dimensional nuclear Overhauser effect (NOE) data observed in Me(2)SO and the information from the tem perature dependence of the amide proton chemical shifts were used as c onstraints in distance geometry calculations, The result suggests that each -(Asn-Pro-Asn-Ala)- tetrapeptide forms a structural unit, a cons iderable population of which exists as unique turnlike structures.