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      Induction and Transcriptional Regulation of Laccases in Fungi

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          Abstract

          Fungal laccases are phenol oxidases widely studied for their use in several industrial applications, including pulp bleaching in paper industry, dye decolourisation, detoxification of environmental pollutants and revalorization of wastes and wastewaters. The main difficulty in using these enzymes at industrial scale ensues from their production costs. Elucidation of the components and the mechanisms involved in regulation of laccase gene expression is crucial for increasing the productivity of native laccases in fungi. Laccase gene transcription is regulated by metal ions, various aromatic compounds related to lignin or lignin derivatives, nitrogen and carbon sources. In this manuscript, most of the published results on fungal laccase induction, as well as analyses of both the sequences and putative functions of laccase gene promoters are reviewed. Analyses of promoter sequences allow defining a correlation between the observed regulatory effects on laccase gene transcription and the presence of specific responsive elements, and postulating, in some cases, a mechanism for their functioning. Only few reports have investigated the molecular mechanisms underlying laccase regulation by different stimuli. The reported analyses suggest the existence of a complex picture of laccase regulation phenomena acting through a variety of cis acting elements. However, the general mechanisms for laccase transcriptional regulation are far from being unravelled yet.

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          Most cited references92

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          Laccases: a never-ending story.

          Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) are blue multicopper oxidases that catalyze the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. In fungi, laccases carry out a variety of physiological roles during their life cycle. These enzymes are being increasingly evaluated for a variety of biotechnological applications due to their broad substrate range. In this review, the most recent studies on laccase structural features and catalytic mechanisms along with analyses of their expression are reported and examined with the aim of contributing to the discussion on their structure-function relationships. Attention has also been paid to the properties of enzymes endowed with unique characteristics and to fungal laccase multigene families and their organization.
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            Laccase: new functions for an old enzyme

            A. Mayer (2002)
            Laccases occur widely in fungi; they have been characterized less frequently in higher plants. Here we have focused on more recent reports on the occurrence of laccase and its functions in physiological development and industrial utility. The reports of molecular weights, pH optima, and substrate specificity are extremely diverse. Conclusive proof of the occurrence of laccase in a tissue must demonstrate that the enzyme be able to oxidize quinol with concomitant uptake of oxygen. Laccase is involved in the pigmentation process of fungal spores, the regeneration of tobacco protoplasts, as fungal virulence factors, and in lignification of cell walls and delignification during white rot of wood. Commercially, laccases have been used to delignify woody tissues, produce ethanol, and to distinguish between morphine and codeine. A very wide variety of bioremediation processes employ laccase in order to protect the environment from damage caused by industrial effluents. Research in recent years has been intense, much of it elicited by the wide diversity of laccases, their utility and their very interesting enzymology.
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              The ligninolytic system of the white rot fungus Pycnoporus cinnabarinus: purification and characterization of the laccase.

              The white rot fungus Pycnoporus cinnabarinus was characterized with respect to its set of extracellular phenoloxidases. Laccase was produced as the predominant extracellular phenoloxidase in conjunction with low amounts of an unusual peroxidase. Neither lignin peroxidase nor manganese peroxidase was detected. Laccase was produced constitutively during primary metabolism. Addition of the most effective inducer, 2,5-xylidine, enhanced laccase production ninefold without altering the isoenzyme pattern of the enzyme. Laccase purified to apparent homogeneity was a single polypeptide having a molecular mass of approximately 81,000 Da, as determined by calibrated gel filtration chromatography, and a carbohydrate content of 9%. The enzyme displayed an unusual behavior on isoelectric focusing gels; the activity was split into one major band (pI, 3.7) and several minor bands of decreasing intensity which appeared at regular, closely spaced intervals toward the alkaline end of the gel. Repeated electrophoresis of the major band under identical conditions produced the same pattern, suggesting that the laccase was secreted as a single acidic isoform with a pI of about 3.7 and that the multiband pattern was an artifact produced by electrophoresis. This appeared to be confirmed by N-terminal amino acid sequencing of the purified enzyme, which yielded a single sequence for the first 21 residues. Spectroscopic analysis indicated a typical laccase active site in the P. cinnabarinus enzyme since all three typical Cu(II)-type centers were identified. Substrate specificity and inhibitor studies also indicated the enzyme to be a typical fungal laccase. The N-terminal amino acid sequence of the P. cinnabarinus laccase showed close homology to the N-terminal sequences determined for laccases from Trametes versicolor, Coriolus hirsutus, and an unidentified basidiomycete, PM1. The principal features of the P. cinnabarinus enzyme system, a single predominant laccase and a lack of lignin- or manganese-type peroxidase, make this organism an interesting model for further studies of possible alternative pathways of lignin degradation by white rot fungi.
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                Author and article information

                Journal
                Curr Genomics
                CG
                Current Genomics
                Bentham Science Publishers Ltd
                1389-2029
                1875-5488
                April 2011
                : 12
                : 2
                : 104-112
                Affiliations
                []University of Naples “Federico II”, Dipartimento di Chimica Organica e Biochimica, Complesso Universitario Monte S. Angelo, via Cintia 4, 80126 Napoli, Italy
                Author notes
                [* ]Address correspondence to this author at the University of Naples “Federico II”, Dipartimento di Chimica Organica e Biochimica, Complesso Universitario Monte S. Angelo, via Cintia 4, 80126 Napoli, Italy; Tel: +39 081674315; Fax: +39081674313; E-mail: vfaraco@ 123456unina.it
                Article
                CG-12-104
                10.2174/138920211795564331
                3129044
                21966248
                c7de2108-9104-4d5c-8625-9c02b3d31353
                ©2011 Bentham Science Publishers Ltd.

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.5/), which permits unrestrictive use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 7 February 2011
                : 1 March 2011
                : 14 March 2011
                Categories
                Article

                Genetics
                ace1,nitrogen,promoter,copper,mre,aromatic compounds,xre.
                Genetics
                ace1, nitrogen, promoter, copper, mre, aromatic compounds, xre.

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