Poster Presentation The 42nd Lorne Conference on Protein Structure and Function 2017

Role of lipid interactions in structural and antigenic properties of the C-terminal domain of the malaria antigen MSP2 (#134)

Sreedam C. Das 1 , Chris A. MacRaild 1 , Rodrigo A. V. Morales 1 , Jeffrey Seow 1 , Krishnarjuna Bankala 1 , Ravindu Dissanayake 2 , Robin F. Anders 2 , Raymond S. Norton 1
  1. Department of Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia
  2. Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne , VIC 3086, Australia

Merozoite surface protein 2 (MSP2) is a highly abundant, GPI-anchored antigen on merozoites of the malaria parasite Plasmodium falciparum. It consists of highly conserved N- and C-terminal domains, and a central polymorphic region. All MSP2 alleles are categorized into two families, 3D7 and FC27, based on central variable region sequences, and recombinant MSP2 is highly disordered in solution.1,2 Clinical trials have demonstrated that MSP2, when delivered as an adjuvanted recombinant antigen, is immunogenic and induces responses that are associated with protection from parasite infection.3,4 Nonetheless, little is known about the conformation of MSP2 on the merozoite surface. Since MSP2 is a GPI-anchored surface protein, it may interact with merozoite plasma membrane, which has the potential to change the conformation of native MSP2 and may also affect its antigenicity.5 The interaction of recombinant full-length MSP2 with a range of lipid surfaces has been investigated using high-resolution NMR but detailed structural characterization was impeded by increased line broadening.6,7 Subsequently, a shorter MSP2172-221 consisting of only the C-terminal domain of MSP2 was designed to allow in-depth structural investigation of these interactions and their effect on antigenicity. Chemical shift data indicate that MSP2172-221 and the corresponding residues of full-length FC27 MSP2 have similar conformational properties. The lipid interactions of MSP2172-221 indicate that many residues, including some in epitopes recognised by C-terminal-specific monoclonal antibodies, interact with DPC micelles but there is no indication of a stable helical formation. Binding affinity studies by SPR and ELISA indicate that MSP2172-221 is antigenically similar to full-length MSP2 and show that liposome conjugation alters the antigenicity in a way that may mimic native MSP2 on merozoite surface. These findings highlight the impact of lipid interactions on the conformation and antigenicity of MSP2172-221, and may assist in the design of lipid-conjugated recombinant MSP2 immunogens for use as malaria vaccine candidates.

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