Unlocking the molecular structure of fungal melanin using 13C biosynthetic labeling and solid-state NMR.
Melanins are enigmatic pigments found in all biological kingdoms that are associated with a variety of functions, including microbial virulence. Despite being ubiquitous in nature, melanin pigments have long resisted atomic-level structural examination because of their insolubility and amorphous organization. Cryptococcus neoformans is a human pathogenic fungus that melanizes only when provided with exogenous substrate, thus offering a unique system for exploring questions related to melanin structure at the molecular level. We have exploited the requirement for exogenous substrate in melanin synthesis as well as the capabilities of high-resolution solid-state nuclear magnetic resonance (NMR) to establish the predominantly aliphatic composition of l-dopa melanin and to introduce (13)C labels that permit the identification of proximal carbons in the developing biopolymer. By swelling solid melanin samples in organic solvents and using two-dimensional heteronuclear NMR in conjunction with magic-angle spinning, we have identified chemical bonding patterns typical of alkane, alkene, alcohol, ketone, ester, and indole functional groups. These findings demonstrate the feasibility of a novel approach to determining the structure of melanin using metabolic labeling and NMR spectroscopy.
Tian
Shiying
S
Department of Chemistry, City University of New York Graduate Center and College of Staten Island, Staten Island, New York 1034-6600, USA.
Garcia-Rivera
Javier
J
Yan
Bin
B
Casadevall
Arturo
A
Stark
Ruth E
RE
D002250:Carbon Radioisotopes; D003455:Cryptococcus neoformans / Q000737:chemistry*; D008543:Melanins / Q000737:chemistry*; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular
D002250:Carbon Radioisotopes; D008543:Melanins