Merozoite surface protein 2 of Plasmodium falciparum: Expression, structure, dynamics, and fibril formation of the conserved N‐terminal domain

Abstract

Merozoite surface protein 2 (MSP2) is a GPI-anchored protein on the surface of the merozoite stage of the malaria parasite Plasmodium falciparum. It is largely disordered in solution, but has a propensity to form amyloid-like fibrils under physiological conditions. The N-terminal conserved region (MSP2(1-25)) is part of the protease-resistant core of these fibrils. To investigate the structure and dynamics of this region, its ability to form fibrils, and the role of individual residues in these properties, we have developed a bacterial expression system that yields > or =10 mg of unlabeled or (15)N-labeled peptide per litre of culture. Two recombinant versions of MSP2(1-25), wild-type and a Y7A/Y16A mutant, have been produced. Detailed conformational analysis of the wild-type peptide and backbone (15)N relaxation data indicated that it contains beta-turn and nascent helical structures in the central and C-terminal regions. Residues 6-21 represent the most ordered region of the structure, although there is some flexibility around residues 8 and 9. The 10-residue sequence (MSP2(7-16)) (with two Tyr residues) was predicted to have a higher propensity for beta-aggregation than the 8-mer sequence (MSP2(8-15)), but there was no significant difference in conformation between MSP2(1-25) and [Y7A,Y16A]MSP2(1-25) and the rate of fibril formation was only slightly slower in the mutant. The peptide expression system described here will facilitate further mutational analyses to define the roles of individual residues in transient structural elements and fibril formation, and thus contribute to the further development of MSP2 as a malaria vaccine candidate.

Plasmodium falciparum Merozoite Surface Protein 3

“…Another vaccine candidate merozoite surface protein MSP2, which is a GPI-anchored ϳ30-kDa highly abundant protein, was also shown to form amyloid-like fibrils under physiological conditions as observed for MSP3 in this study (50,51). Structurally, MSP2 has two conserved domains at the N and C termini but is highly polymorphic in the central region.…”

Sequential Processing of Merozoite Surface Proteins during and after Erythrocyte Invasion by Plasmodium falciparum

“…Importantly, both the 3D7 and FC27 allelic forms of MSP2 showed the same phenotype of being carried into RBCs followed by rapid degradation. The 3D7 and FC27 alleles of MSP2 share N-and C-terminal regions but vary significantly in the central strain-specific region of the protein (46,(76)(77)(78). The observation that both MSP2 variants show the same localization and very precise timing of degradation postinvasion suggests that the functions of the 3D7 and FC27 forms of MSP2 are the same, despite any structural differences.…”

Antigenic Characterization of an Intrinsically Unstructured Protein, Plasmodium falciparum Merozoite Surface Protein 2

“…One of these MAbs, 6D8, is the only MAb identified that reacts with the short conserved N-terminal region of MSP2, which was previously established to be responsible for the formation of amyloid-like fibrils by MSP2 (1,30). The failure to detect this epitope on the merozoite surface was not due to removal of this region of MSP2 by proteolytic processing because polyclonal rabbit antibodies to the N-terminal conserved region of the antigen did react with the merozoite surface by IFA (data not shown).…”