Mr Jeffrey Seow (Monash University)
Merozoite surface protein 2 (MSP2) is an unstructured protein of the Plasmodium falciparum merozoite. The two allelic forms of MSP2, 3D7 and FC27, differ in a central variable region which is flanked by conserved N- and C-terminal regions. Vaccine trials using 3D7-MSP2 have shown evidence of strain specific protection despite the detectable presence of conserved region antibodies. This work focuses on an N-terminal epitope recognised by the mouse monoclonal antibody, 6D8. Despite recognising a fully conserved epitope, 6D8 shows strain specificity. Understanding the determinants of 6D8 specificity will assist the designing of a broad-spectrum MSP2-based malaria vaccine. 6D8 was re-engineered into antibody fragments (scFv and Fv) and validated by SPR and ITC. Additionally, a series of N-terminal peptides were synthesised to locate the minimal binding region (NAYNMSIRR, KD = 6 nM) and investigate the strain specificity of 6D8. High-resolution (1.2 Å) crystal structures of four N-terminal peptides bound to 6D8 Fv revealed identical binding mechanisms irrespective of N- or C-terminal extensions from the minimal epitope. However, binding data indicates that the strain specificity of 6D8 to 3D7 and FC27-MSP2 requires the first 5 C-terminal residues of the variable region, and suggest that entropic effects of unbound variable residues determine the strain specificity of 6D8. This progress will underpin the design of effective strain-transcending MSP2-based malaria vaccines and may have wider implications for our understanding of the immune response towards unstructured proteins.
|Keywords or phrases (comma separated)||Immune system, Untructured antigens, Malaria, Vaccine, MSP2, Strain specificity|