Limits...
A coarse-grained model for synergistic action of multiple enzymes on cellulose.

Asztalos A, Daniels M, Sethi A, Shen T, Langan P, Redondo A, Gnanakaran S - Biotechnol Biofuels (2012)

Bottom Line: We present a coarse-grained stochastic model for capturing the key events associated with the enzymatic degradation of cellulose at the mesoscopic level.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA. gnana@lanl.gov.

ABSTRACT

Background: Degradation of cellulose to glucose requires the cooperative action of three classes of enzymes, collectively known as cellulases. Endoglucanases randomly bind to cellulose surfaces and generate new chain ends by hydrolyzing β-1,4-D-glycosidic bonds. Exoglucanases bind to free chain ends and hydrolyze glycosidic bonds in a processive manner releasing cellobiose units. Then, β-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 catalysis occurs on the surface of crystalline cellulose, several factors affect the overall hydrolysis. Therefore, spatial models of cellulose degradation must capture effects such as enzyme crowding and surface heterogeneity, which 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 the qualitative behavior 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.

No MeSH data available.


Related in: MedlinePlus

(a) Effect of initial concentration of endo-cellulase on hydrolysis of cellulose. Change in conversion time as the initial enzyme concentration is varied.(b) Time course of enzyme adsorption. The inset shows the percentage of adsorbed enzymes as a function of time. The cellulose layer is composed of five glucan chains, each of them composed of 5000 glucose units.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3475064&req=5

Figure 8: (a) Effect of initial concentration of endo-cellulase on hydrolysis of cellulose. Change in conversion time as the initial enzyme concentration is varied.(b) Time course of enzyme adsorption. The inset shows the percentage of adsorbed enzymes as a function of time. The cellulose layer is composed of five glucan chains, each of them composed of 5000 glucose units.

Mentions: The effect of varying the initial [E]0 cellulase concentration upon conversion times is plotted in Figure 8a. As the enzyme concentration increases, the gap between the time to convert 50% and 75% of the cellulose substrate decreases. At high enzyme loading (> 22 μM), the conversion time reaches a constant value as the substrate is saturated by adsorbed enzymes: already bound enzymes mutually obstruct the adsorption of additional enzymes onto the surface. As the substrate is reduced over time, the number of available binding sites also decreases, thus fewer and fewer enzymes are able to bind to the surface. This trend is captured in Figure 8b. Cellulases quickly adsorb onto the surface at early times in the hydrolysis process (not shown because of the small time scale), after which their number follows a Poisson decay, and desorption is modeled as a Poisson process. The inset from Figure 8b shows the decrease in bound enzyme percentage as the initial enzyme concentration increases. Although this decrease is relatively small, it underlines the finite size effect of the substrate, which is consistent with Figure 8a.


A coarse-grained model for synergistic action of multiple enzymes on cellulose.

Asztalos A, Daniels M, Sethi A, Shen T, Langan P, Redondo A, Gnanakaran S - Biotechnol Biofuels (2012)

(a) Effect of initial concentration of endo-cellulase on hydrolysis of cellulose. Change in conversion time as the initial enzyme concentration is varied.(b) Time course of enzyme adsorption. The inset shows the percentage of adsorbed enzymes as a function of time. The cellulose layer is composed of five glucan chains, each of them composed of 5000 glucose units.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475064&req=5

Figure 8: (a) Effect of initial concentration of endo-cellulase on hydrolysis of cellulose. Change in conversion time as the initial enzyme concentration is varied.(b) Time course of enzyme adsorption. The inset shows the percentage of adsorbed enzymes as a function of time. The cellulose layer is composed of five glucan chains, each of them composed of 5000 glucose units.
Mentions: The effect of varying the initial [E]0 cellulase concentration upon conversion times is plotted in Figure 8a. As the enzyme concentration increases, the gap between the time to convert 50% and 75% of the cellulose substrate decreases. At high enzyme loading (> 22 μM), the conversion time reaches a constant value as the substrate is saturated by adsorbed enzymes: already bound enzymes mutually obstruct the adsorption of additional enzymes onto the surface. As the substrate is reduced over time, the number of available binding sites also decreases, thus fewer and fewer enzymes are able to bind to the surface. This trend is captured in Figure 8b. Cellulases quickly adsorb onto the surface at early times in the hydrolysis process (not shown because of the small time scale), after which their number follows a Poisson decay, and desorption is modeled as a Poisson process. The inset from Figure 8b shows the decrease in bound enzyme percentage as the initial enzyme concentration increases. Although this decrease is relatively small, it underlines the finite size effect of the substrate, which is consistent with Figure 8a.

Bottom Line: We present a coarse-grained stochastic model for capturing the key events associated with the enzymatic degradation of cellulose at the mesoscopic level.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA. gnana@lanl.gov.

ABSTRACT

Background: Degradation of cellulose to glucose requires the cooperative action of three classes of enzymes, collectively known as cellulases. Endoglucanases randomly bind to cellulose surfaces and generate new chain ends by hydrolyzing β-1,4-D-glycosidic bonds. Exoglucanases bind to free chain ends and hydrolyze glycosidic bonds in a processive manner releasing cellobiose units. Then, β-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 catalysis occurs on the surface of crystalline cellulose, several factors affect the overall hydrolysis. Therefore, spatial models of cellulose degradation must capture effects such as enzyme crowding and surface heterogeneity, which 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 the qualitative behavior 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.

No MeSH data available.


Related in: MedlinePlus