A pair of esterases from a commensal gut bacterium remove acetylations from all positions on complex β-mannans

Significance Acetylation is an important feature of hemicellulose, altering the physical properties of the plant cell wall and limiting enzyme accessibility. Removal of acetyl groups from β-mannan is a key step toward efficient utilization of this glycan as a carbon source for gut microbiota and in biorefineries. We present detailed insight into mannan deacetylation by two highly substrate-specific acetyl-mannan esterases (AcMEs) from a prevalent gut commensal Firmicute, which cooperatively deacetylate complex galactoglucomannan. The three-dimensional structure ofRi CE17 with mannopentaose in the active site has a unique two-domain architecture including a CBM35 and a SGNH superfamily hydrolytic domain. Discovery of β-mannan-specific esterases improves the understanding of an important step in dietary fiber utilization by gut commensal Firmicutes.