Department of Chemical and Biological Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
Yeast. 2011 Mar;28(3):181-8. doi: 10.1002/yea.1829. Epub 2010 Nov 25.
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.
植物中的漆酶活性导致形成许多棕色色素，通常称为单宁。漆酶依赖性色素的产生也在许多真菌和细菌物种中得到了分类。在有外源性底物存在的情况下，单倍体酵母新生隐球菌的漆酶在细胞壁外形成类似于黑色素的色素沉着。虽然这个过程是其在人类中致病的一个因素，但漆酶功能的进化意图仍然是一个谜。我们在这里表明，新生隐球菌和枯草芽孢杆菌能够从各种黄酮类分子中产生类似于黑色素的色素，偏爱那些具有 3'，4'-二羟基化的分子。由于类黄酮是普遍存在的植物分子，通常被认为是抗菌剂，我们推测它们是漆酶活性的预期天然靶标，并导致形成防御性的类似于黑色素的涂层。这些结果表明，黄酮类-黑色素形成可能发生一种新的机制，不仅使用 A-和 C-环键合，而且还通过黄酮类结构的 B-环进行单体键合。我们还表明，白藜芦醇和其他非和单羟基化多酚底物具有限制色素形成的能力，可能是漆酶活性的有效抑制剂。
