title: Solid-state NMR Reveals the Carbon-based Molecular Architecture of Cryptococcus neoformans Fungal Eumelanins in the Cell Wall.
abstract: Melanin pigments protect against both ionizing radiation and free radicals and have potential soil remediation capabilities. Eumelanins produced by pathogenic Cryptococcus neoformans fungi are virulence factors that render the fungal cells resistant to host defenses and certain antifungal drugs. Because of their insoluble and amorphous characteristics, neither the pigment bonding framework nor the cellular interactions underlying melanization of C. neoformans have yielded to comprehensive molecular-scale investigation. This study used the C. neoformans requirement of exogenous obligatory catecholamine precursors for melanization to produce isotopically enriched pigment "ghosts" and applied 2D (13)C-(13)C correlation solid-state NMR to reveal the carbon-based architecture of intact natural eumelanin assemblies in fungal cells. We demonstrated that the aliphatic moieties of solid C. neoformans melanin ghosts include cell-wall components derived from polysaccharides and/or chitin that are associated proximally with lipid membrane constituents. Prior to development of the mature aromatic fungal pigment, these aliphatic moieties form a chemically resistant framework that could serve as the scaffold for melanin synthesis. The indole-based core aromatic moieties show interconnections that are consistent with proposed melanin structures consisting of stacked planar assemblies, which are associated spatially with the aliphatic scaffold. The pyrrole aromatic carbons of the pigments bind covalently to the aliphatic framework via glycoside or glyceride functional groups. These findings establish that the structure of the pigment assembly changes with time and provide the first biophysical information on the mechanism by which melanin is assembled in the fungal cell wall, offering vital insights that can advance the design of bioinspired conductive nanomaterials and novel therapeutics.
authors.affiliation: From the Department of Chemistry, City College of New York, Graduate Center and Institute for Macromolecular Assemblies, City University of New York, New York, New York 10031-9101.
authors.forename: Subhasish
authors.initials: S
authors.lastname: Chatterjee
authors.affiliation: the Department of Microbiology and Immunology, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, and.
authors.forename: Rafael
authors.initials: R
authors.lastname: Prados-Rosales
authors.affiliation: the New York Structural Biology Center, New York, New York 10027.
authors.forename: Boris
authors.initials: B
authors.lastname: Itin
authors.affiliation: the Department of Microbiology and Immunology, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, and.
authors.forename: Arturo
authors.initials: A
authors.lastname: Casadevall
authors.affiliation: From the Department of Chemistry, City College of New York, Graduate Center and Institute for Macromolecular Assemblies, City University of New York, New York, New York 10031-9101, stark@sci.ccny.cuny.edu.
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Stark
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002473:Cell Wall / Q000737:chemistry*; D003455:Cryptococcus neoformans / Q000737:chemistry*; D016503:Drug Delivery Systems; D005609:Free Radicals / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D005989:Glycerides / Q000737:chemistry; D007211:Indoles / Q000737:chemistry; D007980:Levodopa / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008543:Melanins / Q000737:chemistry*; D010858:Pigmentation; D011134:Polysaccharides / Q000737:chemistry; D037521:Virulence Factors / Q000737:chemistry
chemical_list: D005609:Free Radicals; D005989:Glycerides; D007211:Indoles; D008543:Melanins; D011134:Polysaccharides; D037521:Virulence Factors; C041877:eumelanin; D007980:Levodopa; D002244:Carbon; D005947:Glucose
keywords: Cryptococcus neoformans; biomaterials; biophysics; eumelanin; fungal melanin; fungi; melanogenesis; solid state NMR; structural biology
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