title: Characterization of the Dielectric Constant in the Trichoderma reesei Cel7B Active Site.
abstract: An attempt is made to evaluate the dielectric constant of the Trichoderma reesei Cel7B active site. Through kinetic measurements, the pKa value of the catalytic acid E201 is determined. Mutations (away from E201) with net charge changes are introduced to perturb the E201 pKa. It is shown that the mutation with a +1 charge change (including G225R, G230R, and A335R) decreases the pKa of E201, whereas the mutation with a -1 charge change (including Q149E, A222D, G225D, and G230D) increases the pKa. This effect is consistent with the electrostatic interaction between the changed charge and the E201 side chain. The fitting of the experimental data yields an apparent dielectric constant of 25-80. Molecular dynamics simulations with explicit water molecules indicate that the high solvent accessibility of the active site contributes largely to the high dielectric constant. ONIOM calculations show that high dielectric constant benefits the catalysis through decreasing the energy of the transition state relative to that of the enzyme substrate complex.
authors.affiliation: †Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong, 266061, China.
authors.forename: Xiangfei
authors.initials: X
authors.lastname: Song
authors.affiliation: †Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong, 266061, China.
authors.forename: Yefei
authors.initials: Y
authors.lastname: Wang
authors.affiliation: †Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong, 266061, China.
authors.forename: Shujun
authors.initials: S
authors.lastname: Zhang
authors.affiliation: ‡College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao, Shandong, 266109, China.
authors.forename: Shihai
authors.initials: S
authors.lastname: Yan
authors.affiliation: †Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong, 266061, China.
authors.forename: Tong
authors.initials: T
authors.lastname: Li
authors.affiliation: †Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong, 266061, China.
authors.forename: Lishan
authors.initials: L
authors.lastname: Yao
mesh_terms: D055162:Biocatalysis; D020134:Catalytic Domain; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017097:Electric Impedance; D056004:Molecular Dynamics Simulation; D009154:Mutation; D055672:Static Electricity; D014242:Trichoderma / Q000201:enzymology*
chemical_list: D002480:Cellulase