Crystal structure of a feruloyl esterase belonging to the tannase family: A disulfide bond near a catalytic triad

Abstract

Feruloyl esterase (FAE) catalyzes the hydrolysis of the ferulic and diferulic acids present in plant cell wall polysaccharides, and tannase catalyzes the hydrolysis of tannins to release gallic acid. The fungal tannase family in the ESTHER database contains various enzymes, including FAEs and tannases. Despite the importance of FAEs and tannases in bioindustrial applications, three-dimensional structures of the fungal tannase family members have been unknown. Here, we determined the crystal structure of FAE B from Aspergillus oryzae (AoFaeB), which belongs to the fungal tannase family, at 1.5 Å resolution. AoFaeB consists of a catalytic α/β-hydrolase fold domain and a large lid domain, and the latter has a novel fold. To estimate probable binding models of substrates in AoFaeB, an automated docking analysis was performed. In the active site pocket of AoFaeB, residues responsible for the substrate specificity of the FAE activity were identified. The catalytic triad of AoFaeB comprises Ser203, Asp417, and His457, and the serine and histidine residues are directly connected by a disulfide bond of the neighboring cysteine residues, Cys202 and Cys458. This structural feature, the "CS-D-HC motif," is unprecedented in serine hydrolases. A mutational analysis indicated that the novel structural motif plays essential roles in the function of the active site.

The Synthetic Potential of Fungal Feruloyl Esterases: A Correlation with Current Classification Systems and Predicted Structural Properties

“…Homology modeling was performed based on a template structure with high sequence identity. In particular, the tannase-related SF1-3 FAEs showed high homology with the FAE B (AoFaeB) from Aspergillus oryzae [33] while SF6 acetyl xylan related-FAEs showed homology with an acetyl xylan esterase from Aspergillus luchuensis [34]. The SF5 acetyl-xylan-related FAEs showed no significant homology with determined structures (<30%), therefore, this intriguing group was not used for the prediction of surface properties and SMD simulations.…”

“…Production of MtFae1a and FoFaeC was done as described previously [32,33]. P. pastoris transformants containing FAEs from Aspergillus species, Ceriporiopsis subvermispora, and Galerina marginata were grown according to previous reports [26,28,30,32].…”

“…Results were evaluated based on the resulting binding energy (more positive energies indicate stronger binding and negative energies mean no binding), the number of genetic runs per cluster, the orientation of the ligand per cluster, and the distance of carbonyl carbon from the catalytic serine of the cluster resulting in a catalytic orientation. This was determined according to Suzuki et al [33] based on the co-crystallization of FA with AnFaeA from Aspergillus niger [42] where the hydroxycinnamate moiety of the ligand is placed in the binding pocket while the substitution is extending outside the pocket. Ligand-receptor complexes were visualized and surface properties were calculated by YASARA [43].…”

Characterization of a feruloyl esterase B from Talaromyces cellulolyticus

“…Recently, a feruloyl esterase B from Aspergillus oryzae (AoFaeB) was purified and characterized functionally and structurally. 32) TcFaeB exhibits low amino acid sequence identity to AoFaeB (around 10%; Fig. 1).…”

“…The family of Esterase_phb contains two species of depolymerases for poly(3-hydroxybutyrate) (PHB) and related polyhydroxyalkanoates, as well as acetyl xylan esterases, and feruloyl esterases from fungi. 32) PHB is produced from the hydrolysis of [(R)-3-hydroxybutanoic acid] n by PHB depolymerase (EC 3.1.1.75). The catalytic mechanism of the PHB depolymerase has been clarified from the crystal structure of PHB depolymerase from Penicillium (Talaromyces) funiculosum (TfPhb).…”