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Blue and non-blue laccases of basidiomycetes

Ziel

Laccase is a copper containing blue oxidase capable of oxidation of a wide range of substrates. In accompany with special synthetic or natural compounds (redox-mediators) laccase becomes capable of reaction with highly persistent compounds, not normally oxidized by this enzyme. Ligninolytic basidiomycetes (white rot fungi) produce laccases with the highest redox-potential. This suggests that fungal laccase/mediator pair is one of the most powerful oxidants of natural origin, interesting as object of fundamental studies, as well as potential agent for biotechnological applications, already tested for waste waters treatment, transformation of xenobiotics, textile fibres or paper pulp bleaching.

Although laccase is a relatively well-known enzyme, only very recently the crystal structure of a laccase from a wood-rotting basidiomycete fungus has been published. Recently the Russian partner in collaboration with Finnish partner, and the Italian partner found new forms of "yellow" and "white" fungal laccases, respectively. These enzymes had unusual spectral properties, but these non-blue laccases were active. The yellow forms catalyzed reactions with persistent compounds, normally not oxidized by blue laccases, without addition of mediators.

Aromatic compounds, which were suggested to affect the activity of the enzyme, may originate from the natural lignocellulosics such as straw or wood. These compounds may attach in the enzyme protein and affect spectral properties, and possibly act as mediators for oxidation of polymeric substances like lignin. Unusual enzymes may also have differences in the topology and composition of the copper-binding sites (in particular Cu-I and Cu-II) within the enzyme proteins. They may be caused by differences in the amino acid sequences of the respective laccase variants.

The main objective of this study is to clarify the true nature of new non-blue laccases compared to classic blue enzymes.
The main tasks (with participating partners in parenthesis) of the proposed work are: (i) to determine the species specificity and ecological dependence of laccase in white-rot fungi (mostly by Russian partners using their large fungal culture collections); (ii) to determine the conditions of growth and development of selected white-rot fungal strains for high laccases production and formation of unusual forms of laccases (all partners); (iii) to compare spectral and catalytic properties of blue, yellow and white laccases of white rot fungi (mostly by Russian partner); (iv) to study of structure of laccase genes and proteins to find out the genetic and structural basis for the production of unusual forms of laccases; homology modelling and attempts to crystallize the enzyme protein will be done (mostly by Italian, but also by Finnish and Russian partners); and (v) to study the presence of aromatic substrate compounds on the unusual spectral properties and reactions catalyzed by the enzymes (Russian partner).

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University of Helsinki
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Viikinkaari 9
00014 Helsinki
Finnland

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