Abstract: Laccases catalyze the oxidative polymerization or degradation of lignin,which plays an important role in the global carbon cycle.Their catalytic mechanism has attracted much attention in the field of biomass science.In the investigation,a 3D model of Myceliophthora thermophila (Mth) laccase was constructed by means of the in-sili- co molecular simulation,and then the docking experiments of nine lignin model compounds were performed in the region of T₁ copper active pocket in the Mth laccase.The results show that (1) the four copper ions in the Mth lac- case are bound with four highly-conserved amino acid fragments; (2) the Mth laccase and the Melanocarpus albo- myces (Mal) laccase have the nearest phylogenetic relationship with an identity of over 74%,and by the Mal lac- case as template,a high-quality model of Mth laccase can be constructed; (3) the Ramachandran plot analysis proves that the confirmations of all amino acid residues are reasonable and correct; (4) within the T₁ copper active pocket in the Mth laccase,monolignol units are bound with Ala₁₉₂ ,Lys₁₈₈ and Trp₅₀₇ through hydrogen bonding; (5) the carboxylation of the monolignol side chain will influence the formation of the hydrogen bonds at Trp₅₀₇ ,and the substitution with dual methoxyl groups at the ortho-position of phenolics will reduce the binding energy of the monolignol units; (6) the higher the polymerization degree of the lignin model compounds,the lower the binding energy will be,which can be correlated linearly with each other; and (7) due to stereo-hindrance,lignol tetramers cannot enter the active pocket,requiring mediators for the oxidation by the Mth laccase.

Key words: molecular docking, Myceliophthora thermophila laccase, lignin model compounds, active pocket, functional group, binding energy