Fungal Melanin: What do We Know About Structure?

Abstract

The production of melanin significantly enhances the virulence of many important human pathogenic fungi. Despite fungal melanin’s importance in human disease, as well as melanin’s contribution to the ability of fungi to survive in diverse hostile environments, the structure of melanin remains unsolved. Nevertheless, ongoing research efforts have progressively revealed several notable structural characteristics of this enigmatic pigment, which will be the focus of this review. These compositional and organizational insights could further our ability to develop novel therapeutic approaches to combat fungal disease and enhance our understanding of how melanin is inserted into the cell wall.

Production of Melanin Pigment by Fungi and Its Biotechnological Applications

“…Similar results were also observed for melanin from Ophiocordyceps sinensis, which proved to be an effective DPPH radical scavenger and a strong ferrous iron chelator [105]. The chelating power of fungal melanin can be explained by various functional groups present in the structure of this pigment, which provide an array of multiple nonequivalent binding sites for metal ions [14,22].…”

“…This pigment protects the conidia against digestion by proteases and hydrolases secreted by competitive microorganisms or against bactericidal and fungicidal proteins of animal origin, such as defensins, magainins, or protegrins [22]. This effect was observed for Cryptococcus neoformans, whose in vitro melanization has been associated with resistance against host effector cells, oxidants, microbicidal peptides, and amphotericin B [23][24][25], and in melanin [22].…”

“…This pigment protects the conidia against digestion by proteases and hydrolases secreted by competitive microorganisms or against bactericidal and fungicidal proteins of animal origin, such as defensins, magainins, or protegrins [22]. This effect was observed for Cryptococcus neoformans, whose in vitro melanization has been associated with resistance against host effector cells, oxidants, microbicidal peptides, and amphotericin B [23][24][25], and in melanin [22]. Studies have shown that the effect of melanin enhancing the survival of fungi under adverse conditions can be mainly due to its powerful free radical scavenger properties, acting as a "sponge" for other free radicals generated by the fungus in response to environmental stress [20,29,30].…”

Introductory Chapter: Melanin, a Versatile Guardian

“…The main function of melanin is to protect the organism from harmful agents such as ultraviolet (UV) radiation; melanin is capable of dissipating over 99% of absorbed UV light. Additionally, melanin can act as an eicient antioxidant, thus alleviating certain types of intracellular chemical damage, as well as protecting from the efects of high temperatures, heavy metals and oxidizing agents, and can play a role in the virulence of fungal pathogens by protecting them from the host's immune defense mechanisms [1,2]. Certain organisms repurposed melanin for additional protective functions: ink of cephalopods, octopus, squid and cutleish, blackened by melanin, which provides protection from predators [3].…”

Role of laccase in the virulence ofTalaromyces marneffei:A common link between AIDS-related fungal pathogens?

“…16,17 Other activities of laccases include oxidation of transition metals such as Fe II 18 which block macrophage fungicidal activities, and the synthesis of immunosuppressing oxylipid molecules such as prostaglandin E2. 19 The presence of multiple-enzymatic activities have often made it difficult to determine which one contributes to laccase-dependent virulence under a given condition.…”