Impact of Synergy Partner Cel7B on Cel7A Binding Rates: Insights from Single-Molecule Data.

Area of Science:

• Biotechnology and Bioengineering
• Enzymology
• Sustainable Chemistry

Background:

• Enzymatic degradation of cellulosic biomass is key for sustainable biofuel, chemical, and material production.
• Cellobiohydrolases (exocellulases) and endoglucanases work synergistically for efficient cellulose breakdown.
• The precise mechanism of this exo-endo synergy remains incompletely understood.

Purpose of the Study:

• To mechanistically investigate the synergistic interaction between exocellulase Cel7A and endoglucanase Cel7B.
• To quantify the binding kinetics of Cel7A on cellulose, both alone and in the presence of Cel7B.
• To elucidate how Cel7B influences Cel7A's binding dynamics at the single-molecule level.

Main Methods:

• Utilized single-molecule fluorescence microscopy to track fluorescently tagged Cel7A.
• Measured the association (k_ON) and dissociation (k_OFF) rate constants of Cel7A binding to cellulose.
• Compared Cel7A binding kinetics in isolation versus in the presence of unlabeled Cel7B at a 10:1 molar ratio.

Main Results:

• The dissociation rate constant (k_OFF) of Cel7A remained unaffected by the presence of Cel7B.
• The association rate constant (k_ON) of Cel7A significantly decreased by a factor of two when Cel7B was present.
• This reduction in k_ON was observed across a broad range of enzyme concentrations (sub-nM to μM).

Conclusions:

• The observed decrease in Cel7A's association rate (k_ON) in the presence of Cel7B supports the formation of enzyme clusters.
• This finding provides a mechanistic insight into the enhanced cellulose degradation observed in exo-endo synergistic systems.
• Understanding these binding dynamics is crucial for optimizing enzymatic processes in biomass conversion.