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Appl. Environ. Microbiol., 08 1997, 3151-3157, Vol 63, No. 8
RM Berka, P Schneider, EJ Golightly, SH Brown, M Madden, KM Brown, T Halkier, K Mondorf and F Xu
A genomic DNA segment encoding an extracellular laccase was isolated from
the thermophilic fungus Myceliophthora thermophila, and the nucleotide
sequence of this gene was determined. The deduced amino acid sequence of M.
thermophila laccase (MtL) shows homology to laccases from diverse fungal
genera. A vector containing the M. thermophila laccase coding region, under
transcriptional control of an Aspergillus oryzae alpha-amylase gene
promoter and terminator, was constructed for heterologous expression in A.
oryzae. The recombinant laccase expressed in A. oryzae was purified to
electrophoretic homogeneity by anion- exchange chromatography.
Amino-terminal sequence data suggests that MtL is synthesized as a
preproenzyme. The molecular mass was estimated to be approximately 100 to
140 kDa by gel filtration on Sephacryl S-300 and to be 85 kDa by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis. Carbohydrate analysis
revealed that MtL contains 40 to 60% glycosylation. The laccase shows an
absorbance spectrum that is typical of blue copper oxidases, with maxima at
276 and 589 nm, and contains 3.9 copper atoms per subunit. With
syringaldazine as a substrate, MtL has optimal activity at pH 6.5 and
retains nearly 100% of its activity when incubated at 60 degrees C for 20
min. This is the first report of the cloning and heterologous expression of
a thermostable laccase.
Copyright © 1997, American Society for Microbiology
Characterization of the gene encoding an extracellular laccase of Myceliophthora thermophila and analysis of the recombinant enzyme expressed in Aspergillus oryzae
Novo Nordisk Biotech, Inc., Davis, California, USA. ramb@novo.dk
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