The aldo-keto reductase: a multipurpose enzyme for biorefinery applications.

Background: In nature, termites can be considered as a model biological system for biofuel research based on their remarkable efficiency for lignocellulosic biomass conversion. Redox enzymes are of interest in second-generation ethanol production because they promote synergic enzymatic activity with classical hydrolases for lignocellulose saccharification and inactivate fermentation inhibitory compounds produced after lignocellulose pretreatment steps.

Results: In the present study, the biochemical and structural characteristics of the aldo-keto reductase (AKR-1) were comprehensively investigated. AKR-1 displayed major structural differences compared with others AKRs, including the differences in the amino acid composition of the substrate-binding site, providing basis for classification as a founding member of a new AKR subfamily (family AKR1 I). Immunolocalization assays with anti-AKR-1 antibodies resulted in strong fluorescence in the salivary gland, proventriculus, and foregut. AKR-1 supplementation caused a 32% reduction in phenolic aldehydes, such as furfural, which act as fermentation inhibitors of hemicellulosic hydrolysates, and improved ethanol fermentation by the xylose-fermenting yeast by 45%. We observed synergistic enzymatic interactions between AKR-1 and commercial cellulosic cocktail for sugarcane bagasse saccharification, with a maximum synergism degree of 2.17 for sugar release. Our data indicated that additive enzymatic activity could be mediated by reactive oxygen species because AKR-1 could produce hydrogen peroxide.

Conclusion: In summary, we identified the founding member of an AKRI subfamily with a potential role in the termite digestome. AKR-1 was found to be a multipurpose enzyme with potential biotechnological applications. The present work provided a basis for the development and application of integrative and multipurpose enzymes in the bioethanol production chain.