(257c) Cellulase Binding to Insoluble Plant Cell Walls Is Substrate Dependent

Enzyme binding to insoluble cell walls is the first step towards effective deconstruction to monomeric sugars. However, the relationship between cellulase binding and synergistic activity as well as non-productive binding versus productive binding is unclear. We have applied a novel liquid chromatography based method to individually quantify the extent of cellulase (CBH I, CBH II and EG I) binding during the course of enzymatic hydrolysis for various cellulosic substrates. The binding isotherms for single, binary and ternary cellulase mixtures were determined for untreated, Ammonia Fiber Expansion (AFEX) treated and dilute-acid treated corn stover. Other isolated cellulosic substrates such as cellulose Iβ, liquid ammonia treated cellulose (cellulose III), sodium hydroxide treated cellulose (cellulose II) and phosphoric acid swollen cellulose (amorphous) were also studied for their cellulase binding affinities. EG I enhanced CBH binding for AFEX corn stover but not for untreated and dilute-acid pretreated corn stover. The total cellulase binding capacity for pretreated corn stover was higher than untreated corn stover. However, for the more digestible cellulose III, lesser binding was observed compared to native cellulose I. These results have important implications on our understanding of enzyme accessibility and productive binding for pretreated plant cell walls.