Immunogenicity and Protectivity of Plasmodium falciparum EBA-175 Peptide and Its Analog Is Associated with α-Helical Region Shortening and Displacement

Abstract

EBA-175 protein is used as a ligand in the binding of P. falciparum to red blood cells (RBCs). Evidence shows that the conserved peptide 1779 from this protein (with high red blood cell binding ability and known critical erythrocyte binding residues) plays an important role in the invasion process. This peptide is neither immunogenic nor protective; analogs having critical residues replaced by amino acids with similar volume or mass but different polarity were synthesized and inoculated into Aotus monkeys, and elicited different immunogenic and protective responses. Nuclear Magnetic Resonance (1H-NMR) studies revealed that peptide analog 21696 (non-immunogenic and non-protective) presents a large helical fragment, that the peptide 14012 (immunogenic and non-protective) helical fragment is smaller, while the peptide 22812 (immunogenic and protective) alpha-helix is shorter in a different region and possesses greater flexibility at its N-terminus. The presence of methionine residues could affect the structural stability of peptide 22812 and ultimately its immunological response. Our results suggest a new strategy for designing a new malaria multi-component subunit-based vaccine.

Emerging Rules for Subunit-Based, Multiantigenic, Multistage Chemically Synthesized Vaccines

“…41,44,[50][51][52][53][54][55][56][57][58] This distance was 6.5 ( 0.5 Å and 4.5 ( 1.5 Å shorter in short-lived and long-lasting antibody-inducing but non-protection-inducing modified HABPs, respectively, than in immunogenic, protection-inducing ones; residue orientation was also different. 42,43 In essence, immunogenic protection-inducing modified conserved HABPs have been modified so that they can fit perfectly into the MHC II-peptide-TCR complex for triggering an appropriate immune response, providing tremendous support for using chemically synthesized, specifically modified conserved HABPs in vaccine development.…”

Functional, Immunological and Three-Dimensional Analysis of Chemically Synthesised Sporozoite Peptides as Components of a Fully-Effective Antimalarial Vaccine

“…Furthermore, RBC-specific EBA-175 HABPs [73] have been rendered highly immunogenic and protective-immunity inducers in Aotus monkeys once they have been specifically modified [76,134,135].…”

“…A large set of RBC (1779 and 1783) and hepatocyte HABPs (1780, 1781 and 1782) located in the EBA-175 RII fragment are known to establish an intricate H-bond network which is why their 3D structure ( 1 H-NMR) and their location in the RII 3D structure (X-ray crystallography) have also been determined [134,135]. Such 3D structural analysis has confirmed these HABPs' fundamental role in invasion since HABPs 1782 and 1783 have been found to participate in this protein's dimerisation, thereby allowing the formation of the groove in which receptor molecules bind to RBCs.…”

“…6D). We have previously shown that specific modifications made to D358P and K362M's critical binding residues in conserved HABP 1779 [84] has rendered it highly immunogenic and protection-inducing as it has been able to protect monkeys against experimental challenge with the highly virulent Aotusadapted P. falciparum FVO strain [135].…”

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

“…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.…”