Abstract
BackgroundFungal laccases are multicopper oxidases (MCOs) with high biotechnological potential due to their capability to oxidize a wide range of aromatic contaminants using oxygen from the air. Albeit the numerous laccase-like genes described in ascomycete fungi, ascomycete laccases have been less thoroughly studied than white-rot basidiomycetous laccases. A variety of MCO genes has recently been discovered in plant pathogenic ascomycete fungi, however little is known about the presence and function of laccases in these fungi or their potential use as biocatalysts. We aim here to identify the laccase-type oxidoreductases that might be involved in the decolorization of dyes by Leptosphaerulina sp. and to characterize them as potential biotechnological tools.ResultsA Leptosphaerulina fungal strain, isolated from lignocellulosic material in Colombia, produces laccase as the main ligninolytic oxidoreductase activity during decolorization of synthetic organic dyes. Four laccase-type MCO genes were partially amplified from the genomic DNA using degenerate primers based on laccase-specific signature sequences. The phylogenetic analysis showed the clustering of Lac1, Lac4 and Lac3 with ascomycete laccases, whereas Lac2 grouped with fungal ferroxidases (together with other hypothetical laccases). Lac3, the main laccase produced by Leptosphaerulina sp. in dye decolorizing and laccase-induced cultures (according to the shotgun analysis of both secretomes) was purified and characterized in this study. It is a sensu-stricto laccase able to decolorize synthetic organic dyes with high efficiency particularly in the presence of natural mediator compounds.ConclusionsThe searching for laccase-type MCOs in ascomycetous families where their presence is poorly known, might provide a source of biocatalysts with potential biotechnological interest and shed light on their role in the fungus. The information provided by the use of genomic and proteomic tools must be combined with the biochemical evaluation of the enzyme to prove its catalytic activity and applicability potential.Electronic supplementary materialThe online version of this article (doi:10.1186/s12896-015-0192-2) contains supplementary material, which is available to authorized users.
Highlights
Fungal laccases are multicopper oxidases (MCOs) with high biotechnological potential due to their capability to oxidize a wide range of aromatic contaminants using oxygen from the air
Flasks were incubated at 25 °C and 200 rev min−1 and the ligninolytic oxidoreductase activities secreted by Leptosphaerulina sp. were monitored for 16 days
Of the four laccase-type MCO genes found in Leptosphaerulina sp., three encode for ascomycete laccase-like proteins, whereas Lac2 is related to ferroxidases/laccases proteins
Summary
Fungal laccases are multicopper oxidases (MCOs) with high biotechnological potential due to their capability to oxidize a wide range of aromatic contaminants using oxygen from the air. A variety of MCO genes has recently been discovered in plant pathogenic ascomycete fungi, little is known about the presence and function of laccases in these fungi or their potential use as biocatalysts. Multicopper oxidases (MCOs) are a multifaceted group of proteins with diverse functions, ranging from copper and iron metabolism (e.g. ceruloplasmin) to polyphenol oxidation (e.g. laccases), and different domain folding. MCOs catalyze the oxidation of a wide variety of substrates with the concomitant reduction of molecular oxygen to water. In a typical MCO oxidation, the abstraction of four separate electrons takes place at the T1 copper site. Fast intramolecular electron transfer occurs from T1 site to the trinuclear Cu cluster (one T2 and two T3 copper ions) where oxygen binds and is converted to water
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