title: Melanization of flavonoids by fungal and bacterial laccases.
abstract: Laccase activity in plants results in the formation of a number of brown pigments, often referred to as tannins. Laccase-dependent pigment production is also catalogued in numerous fungal and bacterial species. The laccase of the haploid yeast Cryptococcus neoformans forms melanin-like pigmentation outside the cell wall in the presence of exogenous substrates. While this process is a contributing factor to its virulence in humans, the evolutionary intent for the laccase function remains a mystery. We show here that C. neoformans and Bacillus subtilis have the ability to create melanin-like pigments from a variety of flavonoid molecules across a range of conformations, preferring those with 3',4'-dihydroxylations. Since flavonoids are ubiquitous plant molecules and often-considered antimicrobial agents, we postulate that they are the intended natural targets of laccase activity and result in the formation of a defensive melanin-like coat. These results suggests a new mechanism by which flavonoid-melanin formation may occur, using not only A- and C-ring linkages, but also monomer links through the B-ring of the flavonoid structure. We also show that resveratrol and other non- and mono-hydroxylated polyphenol substrates have the ability to restrict pigment formation and may be potent inhibitors of laccase activity.
authors.affiliation: Department of Chemical and Biological Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
authors.forename: Zachary L
authors.initials: ZL
authors.lastname: Fowler
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Baron
authors.forename: John C
authors.initials: JC
authors.lastname: Panepinto
authors.forename: Mattheos A G
authors.initials: MA
authors.lastname: Koffas
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D003455:Cryptococcus neoformans / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005419:Flavonoids / Q000378:metabolism*; D042845:Laccase / Q000378:metabolism*; D008543:Melanins / Q000378:metabolism*; D000077185:Resveratrol; D013267:Stilbenes / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D008543:Melanins; D013267:Stilbenes; D042845:Laccase; D000077185:Resveratrol