Role of F124 in the inhibition of Bacillus firmus K-1 Xyn11A by monomeric aromatic phenolic compounds

Abstract This study aimed to investigate the inhibitory effect of monomeric aromatic phenolic compounds on Xyn11A and its F124A mutant. The inhibitory assay showed gallic acid as the most potent inhibitor for the WT. Conversely, gallic acid completely lost its inhibitory effect and resistance to the other compounds increased significantly in the F124A mutant. Molecular docking revealed that phenolic compounds inhibited WT by simultaneously binding to E78, R112, and F124. The pi-pi stacking of F124 and aromatic rings of phenolic compounds mediated the hydrogen bonds formed between phenolic inhibitors and E78. Gallic acid's strongest inhibitory effects in WT may be due to the high number of hydroxyl groups. However, in F124A, the phenolic compounds bound tyrosine residues sitting far from the catalytic site. Gallic acid's binding to Y69, which is furthest away from the catalytic site and highest specific binding energy, may have contributed to gallic acid's loss of inhibitory effects in F124A.