Comparative characterization of a recombinant Volvariella volvacea endoglucanase I (EG1) with its truncated catalytic core (EG1-CM), and their impact on the bio-treatment of cellulose-based fabrics

Recombinant Volvariella volvacea endoglucanase 1 (EG1) and its catalytic module (EG1-CM) were obtained by expression in Pichia pastoris, purified by two-step chromatography, and the catalytic activities and binding capacities were compared. EG1 and EG1-CM exhibited very similar specific activities towards the soluble substrates carboxymethyl cellulose, lichenan and mannan, and insoluble H₃PO₄ acid-swollen cellulose, whereas the specific activities of EG1-CM towards the insoluble substrates -cellulose, Avicel and filter paper were approximately 58, 43 and 38%, respectively compared to EG1. No increase in reducing sugar release was detected in the reaction mixture supernatants after 50 h exposure of filter paper, Avicel or -cellulose to EG1-CM, whereas increases in the total reducing sugar equivalents (i.e. reducing sugar released into solution together with new reducing ends generated in the cellulosic substrates) in reaction mixtures were observed after 1 h. In reaction mixtures containing EG1, soluble reducing sugar equivalents were detected in supernatants after 3 h incubation with the insoluble cellulosic substrates. EG1-CM did not adsorb to Avicel, and the binding capacities of EG1-CM towards filter paper and H₃PO₄ acid-swollen cellulose were 27.9–33.3% and 29.6–60.6%, respectively of values obtained with EG1 within the range of total added protein. In enzymatic deinking experiments, the ink removal rate in EG1-CM-treated samples was only slightly higher (8%), than that of untreated controls, whereas that of the EG1-treated samples was 100% higher. Bio-stoning of denim with EG1-CM resulted in increases of 48% and 40% in weight loss and indigo dye removal, respectively compared with untreated controls. These increases were considerably lower than the corresponding values of 219% and 133% obtained when samples were treated with EG1.