RT Journal Article SR Electronic T1 The structural unit of melanin in the cell wall of the fungal pathogen Cryptococcus neoformans JF bioRxiv FD Cold Spring Harbor Laboratory SP 644484 DO 10.1101/644484 A1 Emma Camacho A1 Raghav Vij A1 Christine Chrissian A1 Rafael Prados-Rosales A1 David Gil A1 Robert N. O’Meally A1 Radames J.B. Cordero A1 Robert N. Cole A1 J. Michael McCaffery A1 Ruth E. Stark A1 Arturo Casadevall YR 2019 UL http://biorxiv.org/content/early/2019/05/20/644484.abstract AB Melanins are synthesized macromolecules that are found in all biological kingdoms. These pigments have a myriad of roles that range from microbial virulence to key components of the innate immune response in invertebrates. Melanins also exhibit unique properties with potential applications in physics and material sciences, ranging from electrical batteries to novel therapeutics. In the fungi, melanins such as eumelanins, are components of the cell wall that provide protection against biotic and abiotic elements. Elucidation of the smallest fungal cell wall-asociated melanin unit that serves as a building block is critical to understand the architecture of these polymers, its interaction with surrounding components, and their functional versatility. In this study, we used isopycnic gradient sedimentation, NMR, EPR, high-resolution microscopy, and proteomics to analyze the melanin in the cell wall of the human pathogenic fungus Cryptococcus neoformans. We observed that melanin is assembled into the cryptococcal cell wall in spherical structures of ∼200 nm in diameter, termed melanin granules, which are in turn composed of nanospheres of ∼30 nm in diameter, the fungal melanosomes. We noted that melanin granules are closely associated with proteins that may play critical roles in the fungal melanogenesis and the supramolecular structure of this polymer. Using this structural information, we propose a model for C. neoformans melanization that is similar to the process used in animal melanization and is consistent with the phylogenetic relatedness of the fungal and animal kingdoms.