title: Small angle neutron scattering reveals pH-dependent conformational changes in Trichoderma reesei cellobiohydrolase I: implications for enzymatic activity.
abstract: Cellobiohydrolase I (Cel7A) of the fungus Trichoderma reesei (now classified as an anamorph of Hypocrea jecorina) hydrolyzes crystalline cellulose to soluble sugars, making it of key interest for producing fermentable sugars from biomass for biofuel production. The activity of the enzyme is pH-dependent, with its highest activity occurring at pH 4-5. To probe the response of the solution structure of Cel7A to changes in pH, we measured small angle neutron scattering of it in a series of solutions having pH values of 7.0, 6.0, 5.3, and 4.2. As the pH decreases from 7.0 to 5.3, the enzyme structure remains well defined, possessing a spatial differentiation between the cellulose binding domain and the catalytic core that only changes subtly. At pH 4.2, the solution conformation of the enzyme changes to a structure that is intermediate between a properly folded enzyme and a denatured, unfolded state, yet the secondary structure of the enzyme is essentially unaltered. The results indicate that at the pH of optimal activity, the catalytic core of the enzyme adopts a structure in which the compact packing typical of a fully folded polypeptide chain is disrupted and suggest that the increased range of structures afforded by this disordered state plays an important role in the increased activity of Cel7A through conformational selection.
authors.affiliation: Center for Structural Molecular Biology, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Sai Venkatesh
authors.initials: SV
authors.lastname: Pingali
authors.forename: Hugh M
authors.initials: HM
authors.lastname: O'Neill
authors.forename: Joseph
authors.initials: J
authors.lastname: McGaughey
authors.forename: Volker S
authors.initials: VS
authors.lastname: Urban
authors.forename: Caroline S
authors.initials: CS
authors.lastname: Rempe
authors.forename: Loukas
authors.initials: L
authors.lastname: Petridis
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Smith
authors.forename: Barbara R
authors.initials: BR
authors.lastname: Evans
authors.forename: William T
authors.initials: WT
authors.lastname: Heller
mesh_terms: D043366:Cellulose 1,4-beta-Cellobiosidase / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins; D006863:Hydrogen-Ion Concentration; D009502:Neutrons; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D013329:Structure-Activity Relationship; D014242:Trichoderma / Q000201:enzymology*
chemical_list: D005656:Fungal Proteins; D043366:Cellulose 1,4-beta-Cellobiosidase