Laccase-induced HBT-grafting to milled beech wood reduces unspecific protein adsorption

Lignocellulosic biomass is a ubiquitous and renewable feedstock for the production of platform chemicals and biofuels. Typically, this recalcitrant biomass is pretreated by physico-chemical techniques causing disintegration and delignification. An additional treatment with laccase-mediator-systems (LMS) has been found to further improve the subsequent enzymatic cellulose hydrolysis. The aim of this study was to investigate the impact of different LMS on the glucose yield of a subsequent hydrolysis of treated beech wood and to elucidate the underlying effect of LMS treatment. The mediators 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), 1-hydroxybenzotriazol (HBT) and syringaldehyde were evaluated, but an enhancing effect of LMS treatment on beech wood hydrolysis was only found for HBT. In mass spectrometry analysis of the acid hydrolysate of LMS-treated samples, the mediator HBT could be found in the lignin samples, suggesting a grafting reaction. The fluorescent protein mCherry was used as a reporter for unspecific protein adsorption to biomass samples. LMS treatment with HBT reduced the unspecific adsorption of mCherry to raw beech wood by about 50%, suggesting that the HBT grafting to beech wood lignin decreased the unproductive cellulase binding. In summary, the reduction of unspecific protein adsorption by biomass surface modification with laccase-HBT treatment is proposed to be the underlying mechanism for increased cellulose conversion.