Synthesis and assembly of fungal melanin

Abstract

Melanin is a unique pigment with myriad functions that is found in all biological kingdoms. It is multifunctional, providing defense against environmental stresses such as ultraviolet (UV) light, oxidizing agents and ionizing radiation. Melanin contributes to the ability of fungi to survive in harsh environments. In addition, it plays a role in fungal pathogenesis. Melanin is an amorphous polymer that is produced by one of two synthetic pathways. Fungi may synthesize melanin from endogenous substrate via a 1,8-dihydroxynaphthalene (DHN) intermediate. Alternatively, some fungi produce melanin from l-3,4-dihydroxyphenylalanine (l-dopa). The detailed chemical structure of melanin is not known. However, microscopic studies show that it has an overall granular structure. In fungi, melanin granules are localized to the cell wall where they are likely cross-linked to polysaccharides. Recent studies suggest the fungal melanin may be synthesized in internal vesicles akin to mammalian melanosomes and transported to the cell wall. Potential applications of melanin take advantage of melanin's radioprotective properties and propensity to bind to a variety of substances.

Purification and characterisation of a sulphur rich melanin from edible mushroom Termitomyces albuminosus Heim

“…Melanin production helps in protection from extreme environmental conditions such as UV light, ionising radiation, resistance to heat or cold, phagocytosis, heavy metals, and oxidants and provides cell wall rigidity (Money et al 1998; Plonka and Grabacka 2006; Pal et al 2013; Casadevall et al 2017). Despite its importance and ubiquity, many fundamental questions remain unanswered like details of its chemical structure and insolubility (Eisenman and Casadevall 2012). Some fungi undergo melanogenesis in response to certain environmental stress conditions such as extreme temperatures, dessiccation, hyperosmotic conditions, limited nutrients, pH changes, metal toxcicity, UV or ionisation stress, action of antagonistic microbes.…”

“…Fungi synthesise melanin by one of the two synthetic pathways: 1,8-dihydroxynaphthalene (DHN) intermediate and l-3,4-dihydroxyphenylanine (L-DOPA). Melanin synthesis involves copper containing metalloenzymes such as laccase and tyrosinase and in fungi also shows involvement of chitin cross-links to other cell wall polysaccharides and proteins (Eisenman and Casadevall 2012). Studies on melanins in mushrooms are limited to edible mushrooms such as Pleurotus cystidious var.…”

Alternaria alternata transcription factor CmrA controls melanization and spore development

“…The biosynthesis of melanin can follow different biosynthetic routes, among which is the 1,8-dihydroxynaphthalene (DHN) pathway with 1,8-DHN as intermediate (Eisenman & Casadevall, 2012). As in many other fungi, in Al.…”

Coprinopsis atramentaria extract, its organic acids, and synthesized glucuronated and methylated derivatives as antibacterial and antifungal agents

“…21 Melanin production by fungi contributes to the virulence of pathogens of humans as well as those of food crops. 22 It was shown that this pigment has an important role in the protection of the fungus against immune effector cells; it is able to scavenge reactive oxygen species generated by alveolar macrophages and neutrophils of the host.…”