Towards an Understanding of Oxidative Damage in an α-L-Arabinofuranosidase of Trichoderma reesei: a Molecular Dynamics Approach

Trichoderma reesei is a "workhorse" fungus that produces glycosyl hydrolases (e.g., cellulases) at high titers for use in industrial bioprocessing. In this study, we focused on α-L-arabinofuranosidase, an enzyme important for the treatment of lignocellulosic biomass, but susceptible to oxidative damage that can occur during industrial processing. The molecular details that render this enzyme inactive have not yet been identified. To approach this issue, we used proteomics to identify amino acid residues that were oxidized after a relevant oxidative treatment (Fenton reaction). These oxidative modifications were included in the 3D protein structures, and using molecular dynamics simulations, we then studied the behaviors of non-modified and oxidized enzymes. These simulations showed significant alterations of the conformational stability of the protein when oxidized, as evidenced by changes in root mean square deviation (RMSD) and principal component analyses (PCA) trajectories. Likewise, enzyme-ligand interactions such as hydrogen bonds were greatly reduced in quantity and quality in the oxidized protein. Finally, free energy landscape plots showed that there was a more rugged energy surface in the oxidized protein, implying a less favorable reaction pathway. These results reveal the basis for loss of function in this carbohydrate active enzyme (CAZY) in the commercially relevant fungus T. reesei.