Purification and characterization of a thermostable laccase from the ascomycetes Cladosporium cladosporioides and its applications

The fungus Cladosporium cladosporioides was isolated from a coal sample as a dye decolorizing microorganism. The maximum production of laccase from this fungus was found to be 4160 U/I with 0.05 mM CuSO4, 4% (w/v) glucose and lignin 0.04% (w/v). The laccase was purified from C cladosporioides to homogeneity in a very active state using ammonium salt precipitation and gel permeation chromatography. Analysis with SDS-PAGE showed that the purified laccase was a monomeric protein of 71.2 kDa, and the apparent molecular mass of this enzyme was 75.17 kDa (m/z= 75,174), which was accurately determined by MALDI/TOF-MS. The UV-vis absorbance and electron paramagnetic resonance spectra of the purified laccase showed the presence of type 1 and type 3 copper ions. The optimum pH and temperature of the purified laccase were 3.5 and 40-70 degrees C, respectively, and the N-terminal amino acid sequence was determined to be IGPTGDMYIVNEDVS. The purified laccase was effective in the biotransformation of aromatic compounds as well as in the decolorization of various dyes. (C) 2011 Elsevier Ltd. All rights reserved.