11-09: Computational investigation of pH dependence on catalytic function in glycoside hydrolases

Monday, April 29, 2013
Exhibit Hall
Lintao Bu1, Michael F. Crowley2, Michael E. Himmel2 and Gregg T. Beckham1, (1)National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, (2)Biosciences Center, National Renewable Energy Laboratory, Golden, CO
Enzymatic hydrolysis of cellulose via cellulases is significantly pH dependent. Many fungal cellulases function optimally at pH 5 and their activities decrease dramatically at other pHs. Understanding the molecular basis for pH optima is important in engineering cellulases to function optimally at more broadened pH regions to accommodate various sugar upgrading bioprocesses. Here, we use constant pH molecular dynamics simulations to determine the pKa values of titratable residues of a glycoside hydrolase (GH) Family 6 cellobiohydrolase (Cel6A) and a GH Family 7 cellobiohydrolase (Cel7A) from the fungus Hypocrea jecorina. The calculated pKa values of the key catalytic residues in Cel6A and Cel7A confirm their previously proposed roles. Additionally, our results demonstrate that glucose bound in the active sites of Cel6A and Cel7A exhibits distorted conformations at pH 5, while a non-hydrolysable chair conformation is observed at other pHs. Overall, this work provides detailed understanding of the pH optima of cellulases at the molecular level.