Development of bi-functional chimeric enzyme (CtGH1-L1-CtGH5-F194A) from endoglucanase (CtGH5) mutant F194A and β-1,4-glucosidase (CtGH1) from Clostridium thermocellum with enhanced activity and structural integrity

Site-directed mutagenesis of β-1,4-endoglucanase from family 5 glycoside hydrolase (CtGH5) from Clostridium thermocellum was performed to develop a mutant CtGH5-F194A that gave 40 U/mg specific activity against carboxymethyl cellulose, resulting 2-fold higher activity than wild-type CtGH5. CtGH5-F194A was fused with a β-1,4-glucosidase, CtGH1 from Clostridium thermocellum to develop a chimeric enzyme. The chimera (CtGH1-L1-CtGH5-F194A) expressed as a soluble protein using E. coli BL-21cells displaying 3- to 5-fold higher catalytic efficiency for endoglucanase and β-glucosidase activities. TLC analysis of hydrolysed product of CMC by chimera 1 revealed glucose as final product confirming both β-1,4-endoglucanase and β-1,4-glucosidase activities, while the products of CtGH5-F194A were cellobiose and cello-oligosaccharides. Protein melting studies of CtGH5-F194A showed melting temperature (Tm), 68 °C and of CtGH1, 79 °C, whereas, chimera showed 78 °C. The improved structural integrity, thermostability and enhanced bi-functional enzyme activities of chimera makes it potentially useful for industrial application in converting biomass to glucose and thus bioethanol.