title: Improvement of catalytic performance of lignin peroxidase for the enhanced degradation of lignocellulose biomass based on the imbedded electron-relay in long-range electron transfer route.
abstract: BACKGROUND
  Although lignin peroxidase is claimed as a key enzyme in enzyme-catalyzed lignin degradation, in vitro enzymatic degradation of lignin was not easily observed in lab-scale experiments. It implies that other factors may hinder the enzymatic degradation of lignin. Irreversible interaction between phenolic compound and lignin peroxidase was hypothesized when active enzyme could not be recovered after the reaction with degradation product (guaiacol) of lignin phenolic dimer.
  
  
  RESULTS
  In the study of lignin peroxidase isozyme H8 from white-rot fungiPhanerochaete chrysosporium(LiPH8), W251 site was revealed to make the covalent coupling with one moiety of monolignolic radical (guaiacol radical) by LC-MS/MS analysis. Hypothetical electron-relay containing W251 residue was newly suggested based on the observation of repressed radical coupling and remarkably lower electron transfer rate for W215A mutant. Furthermore, the retardation of the suicidal radical coupling between the W251 residue and the monolignolic radical was attempted by supplementing the acidic microenvironment around the W251 residue to engineer radical-robust LiPH8. Among many mutants, mutant A242D showed exceptional catalytic performances by yielding 21.1- and 4.9-fold higher increases of kcatand kcat/KMvalues, respectively, in the oxidation of non-phenolic model lignin dimer.
  
  
  CONCLUSIONS
  A mechanism-based suicide inhibition of LiPH8 by phenolic compounds was firstly revealed and investigated in this work. Radical-robust LiPH8 was also successfully engineered by manipulating the transient radical state of radical-susceptible electron-relay. Radical-robust LiPH8 will play an essential role in degradation of lignin, which will be consequently linked with improved production of sugars from lignocellulose biomass.
authors.affiliation: School of Energy and Chemical Engineering, UNIST, 50 UNIST-gil, Ulju-gun, Ulsan, 44919 Republic of Korea.
authors.forename: Le Thanh Mai
authors.initials: LT
authors.lastname: Pham
authors.affiliation: Life Ingredient Material Research Institute, CJ Company, 42 Gwanggyo-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do Republic of Korea.
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: School of Energy and Chemical Engineering, UNIST, 50 UNIST-gil, Ulju-gun, Ulsan, 44919 Republic of Korea.
authors.forename: Yong Hwan
authors.initials: YH
authors.lastname: Kim
keywords: Lignin peroxidase isozyme H8; Phanerochaete chrysosporium; Radical coupling; Suicide inhibition