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

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.