【For INTERNATIONAL COLLABORATIVE RESEARCH 2016】

DATE: Day 8 Month 5 Year 2017

SUMMARY of
2016 RESEARCH RESULTS REPORTFor International Collaborative Research with IPR, Osaka University
Research Title

Role of transient (fuzzy) interactions and dynamics in theinteraction of an intrinsically disordered malaria vaccine candidate
with the immune system

ApplicantName

Raymond S. Norton

Affiliation

Monash Institute of Pharmaceutical Sciences

Present Title

Professor

Research Collaborator (Host PI)

Toshimichi Fujiwara (Professor)

Summary
Transient (weak) interactions play an essential role in regulating the dynamics of biologicalnetworks. However, it can be difficult to characterise such interactions experimentally, as they are
generally highly dynamic. Nuclear magnetic resonance (NMR) spectroscopy is an excellent methodfor determining the structures of transient complexes and studying their dynamics. This study
focuses on transient interactions that modulate the strain-specificity of a monoclonal antibody (6D8)binding to different allelic forms of a polymorphic malaria antigen, merozoite surface protein 2(MSP2).
MSP2 is an intrinsically disordered protein consisting of conserved N- and C-terminal regions anda variable central region. Based on the variable sequences MSP2 is classified into two alleles, 3D7and FC27. The 6D8 antibody recognizes a highly conserved continuous epitope within the Nterminal region of MSP2, comprised of residues 14-22. Despite binding to this well-defined epitopein a conserved region of the antigen, 6D8 has different affinities for the different allelic forms ofMSP2. This suggests that 6D8 also makes interactions with residues that differ between 3D7 andFC27 MSP2.
Peptides which included the 6D8 epitope and extended into the variable region by 9 residues
recapitulated this affinity difference, indicating that the variable-region residues that are close to thedefined epitope are modulating their binding to 6D8. NMR chemical shift perturbation experiments
were used to identify the 6D8 residues that interact with the MSP2 variable regions in these peptides.
It was found that the perturbed residues in the spectra are distributed across a broad region of the6D8 surface surrounding the paratope suggesting multiple conformations of the variable regions.
The dynamics of the variable regions were studied by performing NMR relaxation experiments on
the extended peptides bound to 6D8. The relaxation data confirm the transient nature of theinteractions and highlight differences in extent or timescale due to the sequence-dependent
conformational preferences of the peptides. The unexpected strain-specificity of the 6D8 antibody
can be explained by differences in these transient interactions. The results from this work contributeto a broader understanding of the role of transient interactions in the binding of disordered antigens
to their cognate antibodies.
*Deadline: May 19, 2017
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