Synthetic peptides as tools to study the capsule of fungal pathogens

Project Outline

Many pathogenic microorganisms produce extracellular polysaccharides that are attached to the cellular surface and are known as capsular polysaccharides. The capsules are a major virulence factor that act by protecting the microorganisms against host immune response and other antimicrobial agents. Among fungal pathogens, the opportunistic species Cryptococcus neoformans is unique in having a large, complex capsule that is responsible for its ability to cause severe infections in humans. Cryptococcus is an emerging global health threat, responsible for more than 200 000 annual deaths worldwide. Current antifungal-based therapies have limited efficacy in eliminating the fungus. Thus, novel therapeutic strategies are greatly needed, but it depends on significant advances in understanding the biology and pathogenesis of Cryptococcus.

The capsule of Cryptococcus plays a key role in modulating the intricate interactions between the fungus and the host, but the precise interactions that can either contribute to or prevent pathogenesis are currently unknown. Many fundamental aspects about the capsule structure-function relationship remain poorly understood, due to the lack of tools to study its complex polysaccharide chemical composition, organization and architecture. Lectins and anti-glycan antibodies are currently the main tools to recognise polysaccharides and provide information about the capsule chemical properties. However, they either lack specificity or are limited on the saccharide chains that they can recognise. Thus, there is the need to develop better tools to specifically recognise a broad spectrum of saccharide chains to significantly improve our knowledge about the structure and function of Cryptococcus capsules.

It is the goal of this interdisciplinary proposed research project to develop glycan-binding peptides that possess high affinity and specificity allowing for studying the molecular structure of the polysaccharides comprising the capsule of Cryptococcus. The peptides will be generated using concepts of molecular recognition, molecular assembly, multivalency and supramolecular chemistry and will incorporate unnatural amino acid side chains featuring the boronic acid functional group. The boronic acid moiety will not only increase the complexity and diversity of the peptides that can be generated but will have a key role in promoting glycan selectivity and affinity. The boronic acid-functionalized peptides will be subsequently employed to create a high-resolution chemical mapping of the Cryptococcus capsule.

References

1. Zaragoza, O.; Rodrigues, M. L.; De Jesus, M.; Frases, S.; Dadachova, E.; Casadevall, A., The Capsule of the Fungal Pathogen Cryptococcus Neoformans. In Advances in Applied Microbiology, Vol 68, Laskin, A. I.; Sariaslani, S.; Gadd, G. M., Eds. 2009; Vol. 68, pp 133-216.
2. Probert, M.; Zhou, X.; Goodall, M.; Johnston, S. A.; Bielska, E.; Ballou, E. R.; May, R. C., A Glucuronoxylomannan Epitope Exhibits Serotype-Specific Accessibility and Redistributes Towards the Capsule Surface During Titanization of the Fungal Pathogen Cryptococcus Neoformans. Infect Immun 2019, 87 (4) e00731-18.
3. Tommasone, S.; Tagger, Y. K.; Mendes, P. M., Targeting Oligosaccharides and Glycoconjugates Using Superselective Binding Scaffolds. Adv. Funct. Mat. 2020, 30 (31) 2002298.

Techniques

• Peptide synthesis.
• Supramolecular chemistry.
• High performance liquid chromatography.
• Isothermal titration calorimetry.
• Live and fixed cell microscopy.
• Super-resolution imaging.
• Flow cytometry.