The third cupredoxin domain of fungal laccase, diphenol oxidase
Diphenol oxidase belongs to the laccase family. It catalyzes the initial steps in melanin biosynthesis from diphenols. Melanin is one of the virulence factors of infectious fungi. In the pathogenesis of C. neoformans, melanin pigments have been shown to protect the fungal cells from oxidative and microbicidal activities of host defense systems. Laccase is a blue multicopper oxidase (MCO) which catalyzes the oxidation of a variety aromatic - notably phenolic and inorganic substances coupled to the reduction of molecular oxygen to water. It has been implicated in a wide spectrum of biological activities and, in particular, plays a key role in morphogenesis, development and lignin metabolism. Although MCOs have diverse functions, majority of them have three cupredoxin domain repeats that include one mononuclear and one trinuclear copper center. The copper ions are bound in several sites: Type 1, Type 2, and/or Type 3. The ensemble of types 2 and 3 copper is called a trinuclear cluster. MCOs oxidize their substrate by accepting electrons at a mononuclear copper center and transferring them to the active site trinuclear copper center. The cupredoxin domain 3 of 3-domain MCOs contains the Type 1 (T1) copper binding site and part the trinuclear copper binding site, which is located at the interface of domains 1 and 3.
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