title: Cryptococcus neoformans capsular polysaccharides form branched and complex filamentous networks viewed by high-resolution microscopy.
abstract: Cryptococcus neoformans is a fungal pathogen that causes life-threatening infections in immunocompromised individuals. Its main virulence factor is an extracellular polysaccharide capsule whose structure, assembly and dynamics remain poorly understood. In this study, we apply improved protocols for sample preparation and recently-developed scanning microscopy techniques to visualize the ultrastructure of the C. neoformans capsule at high-resolution (up to 1 nm) and improved structural preservation. Although most capsule structures in nature consist of linear polymers, we show here that the C. neoformans capsule is a 'microgel-like' structure composed of branched polysaccharides. Moreover, we imaged the capsule-to-cell wall link, which is formed by thin fibers that branch out of thicker capsule filaments, and have one end firmly embedded in the cell wall structure. Together, our findings provide compelling ultrastructural evidence for a branched and complex capsule conformation, which may have important implications for the biological activity of the capsule as a virulence factor.
authors.affiliation: Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil.
authors.forename: Glauber R de S
authors.initials: GR
authors.lastname: Araújo
authors.affiliation: National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil.
authors.forename: Giselle N
authors.initials: GN
authors.lastname: Fontes
authors.affiliation: National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil.
authors.forename: Daniela
authors.initials: D
authors.lastname: Leão
authors.affiliation: Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Gustavo Miranda
authors.initials: GM
authors.lastname: Rocha
authors.affiliation: Laboratório de Pinças Óticas - COPEA, Instituto de Ciências Biomédicas, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Pontes
authors.affiliation: National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil.
authors.forename: Celso
authors.initials: C
authors.lastname: Sant'Anna
authors.affiliation: Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil.
authors.forename: Wanderley
authors.initials: W
authors.lastname: de Souza
authors.affiliation: Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; National Institute of Metrology, Quality and Technology (Inmetro), Duque de Caxias, Rio de Janeiro, Brazil. Electronic address: frases.susana@gmail.com.
authors.forename: Susana
authors.initials: S
authors.lastname: Frases
mesh_terms: D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure*; D003455:Cryptococcus neoformans / Q000378:metabolism / Q000648:ultrastructure*; D005656:Fungal Proteins / Q000378:metabolism; D008853:Microscopy; D011134:Polysaccharides / Q000378:metabolism*; D037521:Virulence Factors
chemical_list: D005656:Fungal Proteins; D011134:Polysaccharides; D037521:Virulence Factors
keywords: C. neoformans; Capsule; Electron microscopy; Fungal virulence; Polysaccharide