13-02: Enzymatic, biophysical and compositional analysis of Clostridium thermocellum cellulosomes

Clostridium thermocellum produces multi-enzyme macromolecules called cellulosomes which can be ~18 nm and >1MDa in molecular weight.  Cellulosomes are capable of efficiently digesting the diverse polysaccharide composition of plant cell walls.  In order to accomplish this type of carbohydrate degradation, various cellulases, hemicellulases, and other enzymes are bound together via their dockerin modules to the cohesin modules of the scaffoldin proteins.  Cellulosomes have been observed bound to the cell surface by secondary scaffoldins or free in solution.  Carbohydrate binding modules (CBMs) on the individual enzymes and scaffoldins enable cellulosomes to bind to the insoluble substrates.  We purified cell-free cellulosomes and characterized the biophysical characteristics by using small angle X-ray scattering, analytical ultracentrifugation, size-exclusion chromatography and native poly-acrylamide gel electrophoresis.  We also investigated the enzymatic properties of the cellulosome by analyzing the digestion of biomass and model cellulose substrates.  We will present the results of our enzymatic and biophysical assays and discuss how these systems can improve the efficiency of converting biomass to sugars for biofuel production.