AN ENZYMATIC TOOL-BOX FOR LIGNIN OXIDATION/DEGRADATION

Lignin is an amorphous polymer characterized by a wide range of molecular mass components, a disordered and branched three-dimensional structure, insoluble in water and in most common solvents. In order to perform lignin degradation, enzymatic treatment could represent an environmentally friendly alternative to chemical methods[1]. The main purpose of this work was to develop an “enzymatic tool-box” for an efficient oxidation and degradation of lignin into aromatic monomers. Biochemical properties of a number of commercial and recombinant ligninolytic oxidative enzymes (laccases, Mn peroxidases and lignin peroxidases) were evaluated under identical experimental conditions, with the final goal to identify interesting biocatalysts for lignin degradation[2]. The effect of pH, temperature, NaCl, DMSO and Tween-80 on the enzymatic activity has been investigated. The activity of novel enzymes, such as the membrane-bound polyphenol oxidase from the marine bacterium Marinomonas mediterranea[3] and a peroxidase produced by Nonomuraea gerenzanensis, was also evaluated[4]. A new high-throughput colorimetric screening to assay the oxidation/degradation of lignin by different enzymes was developed: this method facilitates the identification of optimal conditions for a lignin treatment based on the combined use of various laccases and peroxidases[5]. On this side, coupling the colorimetric assay with a size-exclusion chromatography analysis allows to identify changes in lignin molecular mass distribution due to enzymatic treatment. Notably, the enzymatic tool-box also comprises etherases, cathecol oxidase and demethylase activities. Finally, a chemo-enzymatic process to depolymerise lignin was carried out on lignin linkage model compounds and technical lignins. Altogether, the combination of chemical and enzymatic approaches could represent an innovative and feasible way for valorisation of lignin under mild conditions. This work was done as part of Biorefill (ID42611813) and ValorPlus (no FP7-KBBE-2013-7-613802) projects. [1] Pollegioni, L.; Tonin, F.; Rosini, E. FEBS Journal 2015, 282(7), 1190-1213. [2] Tonin, F.; Melis, R.; Cordes, A.; Sanchez-Amat, A.; Pollegioni, L.; Rosini, E. New Biotechnology 2016, 33(3), 387-398. [3] Tonin, F.; Rosini, E.; Piubelli, L.; Sanchez-Amat, A.; Pollegioni, L. Protein Expression and Purification 2016, (123), 60-69. [4] Casciello, C.; Tonin, F.; Berini, F.; Fasoli, E.; Marinelli, F.; Pollegioni, L.; Rosini, E. Biotechnology Re- ports 2017, (13), 49-57. [5] Tonin, F.; Vignali, E.; Pollegioni, L.; D’Arrigo, P.; Rosini, E. Enzyme and Microbial Technology 2017, (96), 143-150.