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Laccases involved in lignin metabolism: A study on Miscanthus
The ‘second generation' biorefinery strategy using lignocellulosic biomass such as Miscanthus instead of starch and sugar-based materials to produce biofuel is a promising industry. However, the removal of lignin from lignocellulosic biomass has been considered as the primary obstacle. Therefore, changing the composition of plant cell walls via modifying lignin content and/or composition of monolignols in biomass by either breeding or genetic engineering is an attractive strategy to obtain higher biofuel yield. So far, research on lignin biosynthesis in Miscanthus has focused on the transcriptional regulation of monolignol formation. The aim of this research project is to explore the expression and function of laccases in Miscanthus, which can catalyze the polymerization of monolignols into lignin as recently reported.
Laccases belong to the multicopper oxidase family, a group of enzymes that is widespread in fungi, plants, and bacteria. Laccases use O2 as the ?nal electron acceptor rather than H2O2, thereby differentiating laccases from other lignin modifying enzymes such as lignin peroxidase, versatile peroxidases, and manganese peroxidase (AA2).
In fungi, laccases are involved in lignin degradation by oxidizing the terminal phenolic units in lignin. The consecutive cleavage of linkages within the lignin polymer leads to decrease in average molecular weight and release of lignin substructures thereby modifying the properties of lignin such as solubility. Conversely, in higher plants laccases play a necessary and non-redundant role in lignin synthesis. Here, laccase catalyses the polymerization of monolignols, the mechanism being based on the formation of free radical intermediates.
Exploring the functionality of laccases in lignin metabolism of Miscanthus is expected to open alternative strategies for modifying both lignin content and composition by breeding or genetic engineering.