Background:
Degradation of cellulose to glucose requires cooperative action of three enzymes, collectively known as cellulases. Endoglucanases randomly bind to cellulose surface and generate new chain ends by hydrolysing 1,4-beta-D-glycosidic bonds. Exoglucanases bind to free chain ends and hydrolyze glycosidic bonds in a processive manner releasing cellobiose units. Then, beta-glucosidases hydrolyze soluble cellobiose to glucose. Optimal synergistic action of these enzymes is essential for efficient digestion of cellulose. Experiments show that as hydrolysis proceeds and the cellulose substrate becomes more heterogeneous, the overall degradation slows down. As this catalysis occurs on crystalline cellulose surface, several factors contribute to overall hydrolysis of cellulose. Therefore, it requires development of spatial models of cellulose degradation that can capture effects such as enzyme crowding and surface heterogeneity that have been shown to lead to a reduction in hydrolysis rates.
Results:
We present a coarse-grained stochastic model for capturing the key events associated with the enzymatic degradation of cellulose at the mesoscopic level. This functional model accounts for the mobility and action of a single cellulase enzyme as well as the synergy of multiple endo- and exo-cellulases on a cellulose surface. The quantitative description of cellulose degradation is calculated on a spatial model by including free and bound states of both endo- and exo-cellulases with explicit reactive surface terms (e.g., hydrogen bond breaking, covalent bond cleavages) and corresponding reaction rates. The dynamical evolution of the system is simulated by including physical interactions between cellulases and cellulose.
Conclusions:
Our coarse-grained model reproduces qualitative behaviour of endoglucanases and exoglucanases by accounting for the spatial heterogeneity of the cellulose surface as well as other spatial factors such as enzyme crowding. Importantly, it captures the endo-exo synergism of cellulase enzyme cocktails. This model constitutes a critical step towards testing hypotheses and understanding approaches for maximizing synergy and substrate properties with a goal of cost effective enzymatic hydrolysis.Source:
http://www.biotechnologyforbiofuels.com/rss/
Recommendation and review posted by G. Smith
