Laccase from Melanocarpus albomyces binds effectively to cellulose

This presentation demonstrates that a laccase from the thermophilic fungus Melanocarpus albomyces binds effectively to lignocellulose, Avicel and bacterial microcrystalline cellulose (BMCC). Binding to cellulose has previously been demonstrated for enzymes involved in the modification of lignocellulose, however, the adsorption of a laccase on pure cellulose has not been reported before. Binding on lignin was also studied but no adsorption on alkali lignin was observed. A binding isotherm was established with bacterial microcrystalline cellulose. The data points fitted the Langmuir type one-site binding model well, and the binding parameters for maximum binding capacity (Bmax) and relative partition coefficient (Kp) were calculated from the isotherm. The Bmax of 1.94 mol/g was relatively low, as compared to the values for various cellulases, whereas the Kp of 320 1/g, which describes the binding affinity, was clearly higher than the values reported for cellulases. The combination of high affinity and quite low capacity of binding suggests that M. albomyces laccase is able to bind very effectively to BMCC, but only on relatively few binding sites. Furthermore, the binding was shown to be reversible and not influenced by non-specific, protein or 0.1-0.5 M Na2SO4. The binding of T. hirsuta and Mauginiella sp. laccases was also studied. No adsorption was detected on BMCC or softwood, suggesting that adsorption onto cellulose is not a general feature among laccases.