Anaerobic Fungal Carbohydrate-Binding Modules Exhibit Preference for Fusion to Hemicellulases and Enhance Their Enzymatic Hydrolysis

As auxiliary components of the carbohydrate active enzymes (CAZymes), carbohydrate-binding modules (CBMs) influence the enzymatic hydrolysis of substrates. To investigate the role of anaerobic fungal CBMs in lignocellulose degradation, an architectural analysis of bacterial and fungal CBM-containing protein sequences was completed. Results indicated that 67.9% of the fungal CBMs were incorporated into the plant-biomass-degrading enzymes and 51.1% of the anaerobic fungal CBMs were biased to be fused with the hemicellulose-degrading enzymes. Based on the transcriptomic data of anaerobic fungus Pecoramyces ruminantium F1, three upregulated CBM-fused hemicellulose-degrading enzyme gene clusters were identified. Results suggested that the fused CBMs retained the enzymatic function of the associated CAZymes. Importantly, the CBM1 domains of acetyl xylan esterase (AxeA16138) and α-L-arabinofuranosidase (AraA02173) possessed a crucial role to promote the xylanase-mediated hydrolysis of hemicellulose. These results demonstrated that anaerobic fungal CBMs harbor substantial potential to enhance hemicellulose degradation.