Modeling adsorption and threading of cellobiohydrolase Cel7A

Enzymatic breakdown of cellulose is an example of heterogeneous catalysis. It follows that a molecular understanding relies on a realistic description of the association of the diffusing species (the enzyme) and the solid sorbent (the substrate). We have studied the thermodynamics and kinetics of this process experimentally and modeled the results to gain insight into different steps of the association process. We found that adsorption of the cellobiohydrolase Cel7A was essentially reversible and also identified possible origins of earlier claims of the opposite. Based on this, we introduced a kinetic model and used this to deconvolute experimental data. Specifically we investigated the kinetic order of the association process with respect to both enzyme and substrate, and derived separate rate constants for the initial adsorption and the subsequent “threading” of the cellulose strand into the active tunnel.