Fig. 5: Molecular structures of Bacteroides spp. esterases.

a Molecular structure of the BeGH43/FAE bifunctional enzyme (pink ribbon). At the N-terminus, the structure of the β,1,4-xylosidase (GH43) from Geobacillus thermoleovorans (gray, PDB 5z5i, RMSD = 2.1 Å for 454 residues) has been overlayed, and at the C-terminus the Lactobacillus plantarum tannase (purple, PDB 4jui, RMSD = 2.0 Å for 243 residues) has been overlayed with (FAE) of BeGH43/FAE. Ligands for the 5z5i and 4jui structures are shown in spheres to label the active sites. b Close-up view of the overlay of the active site of the L. plantarum tannase (purple, PDB 4jui) with the C-terminal ferulic acid esterase (FAE) domain of BeGH43/FAE. Residues within 4.0 Å of gallic acid in the tannase and structurally homologous in the B. eggerthii enzyme are displayed. c Ribbon diagram overlay of the dimeric structures of Bi1033-CE1 (green) and Bi1039-CE1 (purple). The red boxed area highlights the most significant structural deviation between the enzymes, comprising residues 221–233 in Bi1039-CE1 and 220–240 in Bi1033-CE1 which includes a chain break from 227 to 230. d Close-up overlay of the active sites of Bi1033-CE1 (green) and Bi1039-CE1 (purple; chain B which includes a small break as indicated). An overlay of Bi1033-CE1 and Bi1039-CE1 with the cellulosomal xylanase Z C-terminal ferulic acid esterase domain from C. thermocellum (PDB 1jt2) complexed with ferulic acid (black and red) was performed to highlight the active site. The region spanning G291-P300 in blue from Bi1039-CE1 is highlighted as it deviates from Bi1033-CE1 in contributing to the active site. e Close-up view of the putative active site residues in Bi1039-CE1 (purple) and the cellulosomal xylanase Z C-terminal ferulic acid esterase domain from C. thermocellum (yellow, PDD 1jt2) complexed with ferulic acid (black and red). f Close-up view of the putative active site residues in Bi1033-CE1 (green) and the C. thermocellum enzyme with ferulic acid (yellow, black, and red).