Thursday, May 5, 2011: 10:30 AM
Grand Ballroom A, 2nd fl (Sheraton Seattle)
Clostridium thermocellum degrades cellulose and lignocellulosic substrates via a cellulosome complex containing multiple enzymes immobilized on a protein scaffold. We explore the contribution of twelve abundant cellulosomal enzymes from C. thermocellum to overall activity in the absence of a cellulosomal complex and investigate the importance of complex formation using an engineered scaffold1. We furthermore probe the importance of changes in the ratios among the enzymes in natural cellulosomes isolated from C. thermocellum cells grown on pure cellulose vs. cells grown on lignocellulosic biomass2. We used mixed enzymes, engineered complexes and natural cellulosomes to break down cellulose and lignocellulosic biomass without pretreatment, with ammonia fiber expansion (AFEX) pretreatment or with dilute-acid pretreatment. The enzymes immobilized on the engineered scaffolds were found to have significantly higher activity than free enzymes for cellulose but similar activities for lignocellulosic substrates. Natural cellulosomes exhibited significantly higher activity than engineered complexes on all substrates tested, probably due, in part, to the higher diversity of enzymes. The two enzyme ratios examined produced similar results in almost all cases. C. thermocellum cellulosomes gave similar glucan hydrolysis yields on pretreated lignocellulosic substrates as commercial Trichoderma reesei cellulases at high enzyme loadings, although the latter appeared to perform better at lower loadings. Our results characterize the fraction of natural cellulosomal activity exhibited by a set of soluble enzymes and the effect of simplified complex formation relative to natural enzyme complexes.
- Mitsuzawa et al. 2009. J Biotechnol 143(2):139-144
- Raman et al. 2009. PLoS ONE 4(4):e5271