Enhanced Oxidative Degradation of β-O-4 Lignin Model Compound Using Robust Lytic Polysaccharide Monooxygenase-Cobalt...

Lignin is a heteropolymer component of ligno-cellulosic biomass made up of monomers connected together by various linkages, the most common of which is the β-O-4 bond. As previously demonstrated, lytic polysaccharide monooxygenase (LPMO) can catalyse the oxidative cleavage of β-O-4 linkage of lignin model compound guaiacyl glycerol-β guaiacyl ether (GGE). But the enhancement of enzymatic activity and stability remains a critical challenge for biocatalytic lignin valorization. In this study, an LPMO-cobalt phosphate organic-inorganic hybrid nanoflower (Co@LPMO-HNF) was developed as a robust biocatalyst for the cleavage of β-O-4 bond. The Co@LPMO-HNF was biochemically and morphologically characterized. Co@LPMO-HNF displayed an optimum temperature of 100 °C and pH 8, exhibiting 1.65-fold higher activity than free LPMO. The Michaelis-Menten kinetic parameters indicated that the Co@LPMO-HNF had 20 fold higher V_max and 13 fold higher turnover number (k_cat) as compared to free LPMO for GGE. The catalytic efficiency (k_cat/K_m) of Co@LPMO-HNF was found to be 700 M^- 1s^- 1which was significantly comparable to free LPMO (650 M^- 1s^- 1). Notably, Co@LPMO-HNF achieved 97% GGE conversion within 24 h versus 40% for the free enzyme and retained 52% of its activity after four catalytic cycles. This is first study to report the synthesis of LPMO based cobalt phosphate nanoflowers (Co@LPMO-HNF) with enhanced activity and stability for the oxidative cleavage of lignin derived compounds. Thus, LPMO loaded hybrid nanoflowers could be of great potential for the sustainable oxidation of lignin and its model compounds.