Trypanosoma cruzi: Conformational preferences of antigenic peptides bearing the immunodominant epitope of the B13 antigen

Duranti, M. A., Franzoni, L., Sartor, G., Benedetti, A., Iwai, L,. K., Grub er, A., Zingales, B., Guzman, F, Kalil, J., Spisni. A., and Cunha-Neto, E. 1999. Trypanosoma cruzi: Conformational preferences of antigenic peptides b earing the immunodominant epitope of the B13 antigen. Expermental Parasitol ogy 93, 38-44. The Trypanosoma cruzi recombinant protein B13 contains tande mly repeated domains and shows high sensitivity in the serological diagnosi s of Chagas' disease. it has been shown that the immunodominant epitope of B13 is contained in the GDKPSLFGQAAAGDKPSLF-NH2 sequence and that the hexap eptide AAAGDK seems to be the "core" of that epitope. Three peptides contai ning that "core" sequence, one corresponding to the entire repeat motif GDK PSLFGQAAAGDKPSLF-NH2, pB13, and two smaller fragments, FGQAAAGDK-NH2, S4, a nd QAAAGDKPS-NH2, S5, have been tested in competitive ELISA with recombinan t protein B13 in the solid phase against 40 chagasic sera from Brazilian pa tients. The median percentage inhibition for pB13, S4, and S5 were, respect ively, 91, 86, and 68%. The possibility that the distinct antigenic activit y of those peptides correlates with the existence of preferential conformat ional properties has been investigated by CD and NMR spectroscopy. Results indicate their propensity to adopt a helical configuration. centered in the AAAGDK sequence, and whose extent and stability directly correlates with t he peptides' antigenicity. The data are discussed in the light of the exist ence of conformational preferences involving immunodominant epitopes in tan demly repeated antigens. (C) 1999 Academic Press.