Evaluation of substrate specificity and catalytic promiscuity of <i>Bacillus albus</i> cellulase: an insight into <i>in silico</i> proteomic study aiming at enhanced production of renewable energy

Cellulases are enzymes that aid in the hydrolysis of cellulosic fibers and have a wide range of industrial uses. In the present <i>in silico</i> study, sequence alignment between cellulases from different <i>Bacillus</i> species revealed that most of the residues are conserved in those aligned enzymes. Three dimensional structures of cellulase enzymes from 23 different <i>Bacillus</i> species have been predicted and based on the alignment between the modeled structures, those enzymes have been categorized into 7 different groups according to the homology in their conformational folds. There are two structural contents in Gr-I cellulase namely β1-α2 and β3-α5 loops which varies greatly according to their static position. Molecular docking study between the <i>B. albus</i> cellulase and its various cellulosic substrates including xylanoglucan oligosaccharides revealed that residues <i>viz.</i> Phe154, Tyr258, Tyr282, Tyr285, and Tyr376 of <i>B. albus</i> cellulase are significantly involved in formation stacking interaction during enzyme-substrate binding. Residue interaction network and binding energy analysis for the <i>B. albus</i> cellulase with different cellulosic substrates depicted the strong affinity of XylGlc3 substrate with the receptor enzyme. Molecular interaction and molecular dynamics simulation studies exhibited structural stability of enzyme-substrate complexes which are greatly influenced by the presence of catalytic promiscuity in their substrate binding sites. Screening of <i>B. albus</i> in carboxymethylcellulose (CMC) and xylan supplemented agar media revealed the capability of the bacterium in degrading both cellulose and xylan. Overall, the study demonstrated <i>B. albus</i> cellulase as an effective biocatalyst candidate with the potential role of catalytic promiscuity for possible applications in biofuel industries.