Understanding Manganese Peroxidase-Catalyzed Conversion of the Lignin Structure and Its Application for the Polymerization of Kraft Lignin

Manganese peroxidase (MnP) has been well studied for woody biomass degradation. MnP exhibits a biotechnological potential for producing lignin-based materials through Kraft lignin (KL) polymerization. MnP derived from Ceriporiopsis subvermispora (CsMnP) is particularly intriguing as this fungus predominantly utilizes MnP to degrade/modify lignin. Here, we investigated CsMnP's catalytic activity toward the phenolic beta-O-4 ' lignin substructure, utilizing guaiacylglycerol-beta-guaiacyl ether (GGE) as the model substrate. The reaction carried out at 25 degrees C and pH 5 was monitored by RP-HPLC, leading to the isolation of five product peaks (P1 to P5) after 48 h. SEC analysis indicated that compounds in P1 to P5 had higher molecular weights than GGE, suggesting polymerization reactions. NMR analysis of P1 revealed that this compound contains two GGE segments, connected by a 5-5 ' linkage. Furthermore, we demonstrated CsMnP's ability to modify KL at 25 degrees C and pH 5, yielding a product with a 360% higher molecular weight compared to untreated KL after 24 h. NMR spectra revealed the deprotonation of the benzenic ring in KL and polymerization through the possible formation of alpha-5 ', 5-5 ', and 4-O-5 ' linkages. This study offers valuable insights into the enzymatic properties of CsMnP and presents a potential strategy for valorizing KL.