Abstract
Cellulases play a key role in enzymatic routes for degradation of plant cell-wall polysaccharides into simple and economically-relevant sugars. However, their low performance on complex substrates and reduced stability under industrial conditions remain the main obstacle for the large-scale production of cellulose-derived products and biofuels. Thus, in this study a novel cellulase with unusual catalytic properties from sugarcane soil metagenome (CelE1) was isolated and characterized. The polypeptide deduced from the celE1 gene encodes a unique glycoside hydrolase domain belonging to GH5 family. The recombinant enzyme was active on both carboxymethyl cellulose and β-glucan with an endo-acting mode according to capillary electrophoretic analysis of cleavage products. CelE1 showed optimum hydrolytic activity at pH 7.0 and 50 °C with remarkable activity at alkaline conditions that is attractive for industrial applications in which conventional acidic cellulases are not suitable. Moreover, its three-dimensional structure was determined at 1.8 Å resolution that allowed the identification of an insertion of eight residues in the β8-α8 loop of the catalytic domain of CelE1, which is not conserved in its psychrophilic orthologs. This 8-residue-long segment is a prominent and distinguishing feature of thermotolerant cellulases 5 suggesting that it might be involved with thermal stability. Based on its unconventional characteristics, CelE1 could be potentially employed in biotechnological processes that require thermotolerant and alkaline cellulases.
Highlights
In the face of growing energy costs, dwindling fossil resources, environmental pollution and a globalized economy, the large-scale use of biotechnology instead of, or to complement, traditional industrial production processes, in the chemical sector, is viewed as both an opportunity and a necessity to a more social and ecological sustainable energetic matrix [1]
The catalytic domains of cellulases are found in 14 families of glycoside hydrolases that have been classified according to their sequence [7]
Recombinant E. coli cells were spread on plates containing 0.5% (w/v) carboxymethyl cellulose (CMC) as substrate and colonies producing clear hydrolytic halos were selected by staining with Congo red [9]
Summary
In the face of growing energy costs, dwindling fossil resources, environmental pollution and a globalized economy, the large-scale use of biotechnology instead of, or to complement, traditional industrial production processes, in the chemical sector, is viewed as both an opportunity and a necessity to a more social and ecological sustainable energetic matrix [1]. The discovery of new enzymes with higher catalytic efficiency and stability under industrial conditions, and even specialized for the different biomass sources, such as sugar-cane bagasse, may have a revolutionary role in making biofuel production from plant biomass economically viable [3,4]. It is more pronounced when focused on cellulose degradation since cellulases are considered the main bottleneck in biomass breakdown, principally due to very low catalytic efficiency. The catalytic domain of cellulases is associated to one or more carbohydrate-binding modules, which binds to the substrate and increase the catalytic efficiency of some enzymes
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