Comparative Biochemical and Structural Properties of an Industrially Important Biocatalyst Cellobiohydrolase Cel7A from Thermophilic Aspergillus fumigatus

Cellobiohydrolase GH7 (Cel7A) is a crucial component of an efficient cellulase system. High cellulase activity was identified in the secretome of a locally identified fungal strain of Aspergillus fumigatus (NITDGPKA3). To investigate the potentiality of Cel7A as a biocatalyst, we have cloned the gene from isolated strain of A. fumigatus. The enzyme (AfCel7A) was expressed in Pichia pastoris and purified. Biochemical properties of this enzyme have been explored and compared with those of Trichoderma reesei Cel7A (TrCel7A), the primary source of industrial cellulase. Higher catalytic activity (Kcat/KM) in AfCel7A than that in TrCel7A suggested a comparative structural analysis with Cel7A of other fungal origins (GcaCel7A, RemCel7A, ThaCel7A, and HirCel7A), including TrCel7A. Variations mainly were observed in the loop region. The molecular dynamics simulation with cellononaose ligand clearly stated that AfCel7A is more compact and stable than TrCel7A. Binding energy analysis indicated that the binding of AfCel7A with cellulose is more potent than that of TrCel7A. Residues Asn49, Asn103, Asp107, Gln175, Glu212, Asp259, Glu217 are typical for binding cellulose in both AfCel7A and TrCel7A. Overall the biochemical and structural characterisation suggests that AfCel7A is a potential biocatalyst for industrial use.