Predicted conformations for the immunodominant region of the circumsporozoite protein of the human malaria parasite Plasmodium falciparum.

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RESUMO

The circumsporozoite protein of the human malaria parasite Plasmodium falciparum contains multiple tandem repeats of the amino acid sequence Asn-Ala-Asn-Pro. The repeated sequence encompasses the immunodominant region of the protein, and antibodies raised against it are potent inhibitors of invasion and development of sporozoites in cultured hepatocytes. Using a modified build-up procedure, we have explored a large number of possible helical and near-helical conformations of a terminally blocked tetraicosapeptide, consisting of six repeats of the sequence Asn-Ala-Asn-Pro, and conclude that two helical conformations are energetically favored to the exclusion of all others. One of these conformations is longer, thinner, and left-handed and is likely to be adopted in nonpolar environments, while the other is shorter, broader, and right-handed and should be favored in aqueous solutions. We propose that the immunodominant region of the circumsporozoite protein of P. falciparum adopts one of these conformations in vivo.

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