Melanin pathogenicity

Langfelder, K. et al., Biosynthesis of fungal melanins and their importance for human pathogenic fungi, Fungal Genet. Biol., 38, 143, 2003. 

Jacobson ES. 2000. Pathogenic roles for fungal melanins. Clin Microbiol Rev 13 708-717. 

It is interesting to underline that there is another (plant) enzyme which possesses a coordinatively similar dicopper environment catechol oxidase.11 As already mentioned in Chapter 6, Section 3, such an ubiquitous enzyme catalyses the two-electron oxidation by molecular dioxygen of catechols to the corresponding quinones (the so-generated quinones in turn polymerize to form brown polyphenolic catechol melanins, which protect damaged plants from pathogens or insects). 

Melanin is a collective term for brown or black pigments. They are condensates of phenolics and are widely distributed in nature, examples of this diverse chemistry being found in animals, plants and fungi. They perform various roles but in some fungi, notably Pyricularia oryzae and Colletotrichum spp., melanin biosynthesis is an essential feature in pathogenicity, the biosynthesis of melanin in appressorial walls being a requirement for the development of infection hyphae and subsequent penetration of the host epidermis. For example, melanin-deficient mutants of P. oryzae are not pathogenic. 

Jacobson ES, Jenkins ND, Todd JM. Relationship between superoxide dismutase and melanin in a pathogenic fungus. Infect Immun 62 4085-4086, 1994. 

Melanin Biosynthesis Inhibitors. Among the most desirable targets for selective fungitoxic action are those uniquely associated with fungal pathogenicity such as the polyketide pathway to melanin in the fungus Pyricularia oryzae which causes rice blast disease. 

Wheeler MH, Bell AA (1988) Melanins and Their Importance in Pathogenic Fungi. Curr Top Med Mycol 7 338... 

Aggregation and encapsulation, which involve the formation of cellular aggregates that surround pathogens with a posterior deposit of melanin, also frequently coincide with phagocytosis (Rg. 3.3). When the foreign bodies are bigger than the haemocytes, recruited fibroblasts deposit mucopolysaccaride residues and fibrous material to form a glycoprotein-associated reticulum (Ratcliffe et al., 1985). 

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