How Melanin Pigments Insinuate Themselves into Fungal Cell Walls: Molecular Views of a Virulent Biocomposite
Natural brown-black eumelanin pigments confer structural coloration in animals, also serving as robust barriers to ionizing radiation and antifungal drugs. These functions also make them attractive for bio-inspired design: coating materials for drug delivery vehicles, strengtheners for adhesive hydrogel materials, and free radical scavengers for soil remediation. Nonetheless, a molecular-level understanding of melanin development and architecture has remained elusive because of the insoluble, amorphous, and chemically heterogeneous character of these complex polymeric assemblies. Solid-state NMR, often assisted by the incorporation of isotopically enriched feedstocks, has emerged as a powerful spectroscopic approach to probe the proportions and molecular structures of the associated melanin, polysaccharide, and lipid constituents in Cryptococcus neoformans fungal cells – and to relate these attributes to their impact on the formation of potentially virulent melanized assemblies.
Among the findings to be discussed are: (1) the identities of the catecholamine precursors alter the structure of the pigments produced in fungal cells and cell-free preparations; (2) the ability of the fungal cell-wall scaffold to retain melanin pigments depends on the proportions of chitin/chitosan and lipid constituents; (3) the macromolecular carbon- and nitrogen-based architecture of cell-free and fungal melanins includes indole, pyrrole, indolequinone, and open-chain building blocks, with interunit connections that can be monitored as they develop; (4) mobile triglycerides and sterol esters that are found unexpectedly in melanized fungal cell walls could be required to make the pigment ‘stick’ to the cell-wall scaffold and promote virulence.
Hosted by Professor Andy Nieuwkoop
~Coffee/tea will be served prior to the lecture~