Alpha helix shortening in 1522 MSP‐1 conserved peptide analogs is associated with immunogenicity and protection against P. falciparum malaria

Abstract

1522 is a nonimmunogenic conserved high-activity binding peptide (HABP) belonging to Plasmodium falciparum MSP-1 protein N-terminal fragment. The key amino acids in binding to red blood cells (RBC) were identified and replaced by others having similar mass but different charge. Because conserved HABPs are not antigenic nor immunogenic, immunogenicity and protectivity studies were then conducted on them in the Aotus monkey. 1H-NMR studies included the lead peptide 1522 as well as the analogs 9782, 13446, 13448, and 13442 to relate their structure to biological function. All the peptides presented alpha-helical structure, with differences observed in helix location and extension. The nonprotective 1522 peptide was totally helical from the N- to the C-terminus, very similar to nonprotective 13442 and 13448 peptides whose extension was almost totally helical. The 9782 and 13446 protective peptides, however, possessed a shorter helical region where modified critical binding residues were not included. A more flexible region was generated at the C-terminus in those peptides with a shorter helical region, leading to a greater number of conformers. These data suggest that peptide flexibility results in increased interaction with immune system molecules, generating protective immunity.

Mapping the anatomy of a Plasmodium falciparum MSP-1 epitope using pseudopeptide-induced mono- and polyclonal antibodies and CD and NMR conformation analysis

“…In this sense, the role of the P. falciparum MSP-1 ligand in this parasite invasion of RBCs has been well documented, as well as some of its most relevant binding fragments, such as MSP-1 42-61 , MSP-1 202-221 , and MSP-1 1282-1301 (Cubillos et al, 2003;Espejo et al, 2002;Helg et al, 2003;Lioy et al, 2001). The MSP-1 43-53 peptide has also proven to be an immunodominant epitope when included in malaria vaccine formulations assessed in clinical trials (Graves et al, 1998;Patarroyo et al, 1987Patarroyo et al, , 1988.…”

“…Field information and animal handling and housing were performed as previously reported (Cubillos et al, 2003).…”

Elongating modified conserved peptides eliminates their immunogenicity and protective efficacy against P. falciparum malaria

“…Numerous studies of Aotus monkeys being immunised with conserved HABPs have found that they were not immunogenic or protection-inducing since they did not induce the production of antibodies against the parasite or induce protection for these immunised monkeys against experimental challenge with a P. falciparum strain 100% infective for this specie (Bermúdez et al, 2005;Cifuentes et al, 2003a,b;Cubillos et al, 2003;Espejo et al, 2004Espejo et al, , 2001Purmova et al, 2002;Salazar et al, 2002;Torres et al, 2003).…”

“…Such modifications included displacing or shortening native molecule a-helix (Cifuentes et al, 2003b;Cubillos et al, 2003;Espejo et al, 2004;Espejo et al, 2001) or a-helicoid fragment appearing in those native HABPs having a random structure Bermú dez et al, 2005;Bermú dez et al, 2003) or b-turn III distortions (Cifuentes et al, 2003a;Purmova et al, 2002), thus stimulating a considerably improved immune response, increasing antibody titres and inducing protection in some Aotus monkeys against experimental challenge. Table 2 shows Aotus immunisation studies with their respective antibody titres against the parasite (determined by IFA) and their protection capacity regarding experimental challenge.…”

“…Later studies with modified HABPs critical RBC binding residues (previously identified by scanning glycine analogues) showed that modifying some of these conserved HABPsÕ critical binding residues by amino acids having similar mass but opposite polarity made them able to become highly immunogenic and capable of inducing a protection-inducing immune response (Bermú dez et al, 2005;Cifuentes et al, 2003a,b;Cubillos et al, 2003;Espejo et al, 2004Espejo et al, , 2001Purmova et al, 2002;Salazar et al, 2002;Torres et al, 2003).…”