The Binding Interaction Mechanism Of Four Kinds Of Lignin Models With Laccase

Lignin is a natural three-dimensional polymer,which is linked by phenol skeleton monomer Coniferyl alcohol(CA),Sinapyl alcohol(SA),P-coumaryl alcohol(PA)through carbon-carbon bonds,ether bonds,and the like.Owing to the disordered coupling of lignin and the stable chemical combination with lignin,cellulose and hemicellulose,leading to the undegradation of lignin and making lignin degradation a very active research hotspot in the fields of biology,environment and chemistry.The lignin monomer CA/PA/SA can act as a medium between laccase(LAC)and lignin,which indirectly affects the catalyzed oxidation of lignin by laccase.To some extent,Guaiacylglycerol-beta-guaiacyl ether(GG)of Lignin model compounds can replace natural lignin,which affects the interaction between CA/PA/SA and LAC on the degradation of lignin by LAC was investigated.Therefore,we used several spectroscopic methods,electrochemical methods combined with molecular dynamics simulation techniques to study the effect of CA/PA/SA and LAC on the molecular mechanism of LAC degradation of GG.These results are as follows:1.Fluorescence emission spectroscopy was used to study interactions of CA,SA,PA and LAC.The experimental results showed that the wavelength corresponding to the maximum fluorescence intensity of LAC has caused shifts by CA,PA and SA.CA,PA have increased LAC fluorescence intensity,resulting in fluorescence sensitizing effect,while SA has decreased LAC fluorescence intensity,resulting in fluorescence quenching,which indicated that there were interactions between CA,SA,PA and LAC.Since the different structures of CA,PA,SA,there are differences in the effects on LAC.2.The conformations and the amino acid residue microenvironments have changed of LAC after the interaction of CA,SA,PA by the synchronous fluorescence and fluorescence polarization techniques,which further illustrated interactions between CA,SA,PA and LAC.Due to the degree of blue shift of the maximum emission wavelength of CA/PA/SA and LAC was different,Verifying that different structure of CA,PA,and SA had differences in the effects on LAC.3.Through electrochemical methods,it was found that the CA/PA/SA-LAC system had regular redox peaks,indicating that all systems had reversible oxidation-reduction reactions,non-radiative energy transfer and electron transfer.However,the binding constants obtained by the differential pulses vary from system to system,which indicated the different structures of CA,PA,SA had differences in the effects on LAC.4.The particle size and Zeta potential and polarization degree and anisotropy of each system decreased by dynamic light diffraction spectroscopy combined with fluorescence polarization technology,indicating that there were interactions between CA,PA,SA,and LAC,resulting in a closer association of the CA/PA/SA-LAC system.5.Molecular dynamics simulation techniques combined with spectroscopic and electrochemical experiments to obtain the reaction types,types of interactions,and binding free energy of theCA/PA/SA/GG-LAC system.Theoretical and experimental results demonstrated that the relationship between SA and LAC promoted the degradation of lignin model compound GG by LAC,while the interaction between CA/PA-LAC had no obvious or inhibitory effects on the degradation of lignin model compound GG by LAC.It was further verified that the structures of CA,PA and SA were different,and there were certain differences in the effect of LAC.