A “yellow” laccase with “blue” spectroscopic features, from Sclerotinia sclerotiorum

Reported here are the production, purification and characterization of a laccase from the phytophathogenic fungus Sclerotinia sclerotiorum. This laccase is identified by mass spectrometry with a sequence coverage of 74.9% (458/577 AA) revealing that the protein is identical or highly homologous to a predicted oxidoreductase from this species (A7EM18 in the Uniprot database); the closest homologous protein previously isolated from a fungus is the Melanocarpus albomyces, with only 35% identity. The UV–vis spectral features of this laccase classify it as a “yellow” one. The EPR spectrum nevertheless demonstrates resemblance to blue laccases – including the type 1 center not detectable in UV–vis spectra. The presence of type 3 coppers was proven by fluorescence spectrum and by 330 nm band in UV–vis. The purified laccase has an apparent molecular mass of 70 kDa and appears as a monomer. The values of KM and kcat were determined for ABTS, 2,6-dimethoxyphenol, p-phenylenediamine and guaicol and are typical of a laccase. The optimal pH value is around 4 except for ABTS, for which activity is linearly increasing with acidity. The high laccase activity in liquid culture makes S. sclerotiorum a useful source of laccase for practical applications.

► A new laccase was isolated from Sclerotinia sclerotiorum. ► This is the first to be classified as ‘yellow’ based on UV–vis yet ‘blue’ based on EPR. ► This laccase has a sequence not previously annotated as such in S. sclerotiorum. ► Good catalytic parameters and high activity in liquid culture offer promise for applications.