title: Thermodynamic effects of disulfide bond on thermal unfolding of the starch-binding domain of Aspergillus niger glucoamylase.
abstract: The thermodynamic effects of the disulfide bond of the fragment protein of the starch-binding domain of Aspergillus niger glucoamylase was investigated by measuring the thermal unfolding of the wild-type protein and its two mutant forms, Cys3Gly/Cys98Gly and Cys3Ser/Cys98Ser. The circular dichroism spectra and the thermodynamic parameters of binding with beta-cyclodextrin at 25 degrees C suggested that the native structures of the three proteins are essentially the same. Differential scanning calorimetry of the thermal unfolding of the proteins showed that the unfolding temperature t1/2 of the two mutant proteins decreased by about 10 degrees C as compared to the wild-type protein at pH 7.0. At t1/2 of the wild-type protein (52.7 degrees C), the mutant proteins destabilized by about 10 kJ mol(-1) in terms of the Gibbs energy change. It was found that the mutant proteins were quite stabilized in terms of enthalpy, but that a higher entropy change overwhelmed the enthalpic effect, resulting in destabilization.
authors.affiliation: Graduate School of Bioresources, Mie University, Japan.
authors.forename: Hayuki
authors.initials: H
authors.lastname: Sugimoto
authors.forename: Miho
authors.initials: M
authors.lastname: Nakaura
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Kosuge
authors.forename: Kunio
authors.initials: K
authors.lastname: Imai
authors.forename: Hideo
authors.initials: H
authors.lastname: Miyake
authors.forename: Shuichi
authors.initials: S
authors.lastname: Karita
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology*; D001665:Binding Sites; D002942:Circular Dichroism; D004220:Disulfides; D004795:Enzyme Stability; D005087:Glucan 1,4-alpha-Glucosidase / Q000737:chemistry* / Q000235:genetics; D006358:Hot Temperature; D020125:Mutation, Missense; D011485:Protein Binding; D011489:Protein Denaturation; D017434:Protein Structure, Tertiary; D013213:Starch; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000737:chemistry
chemical_list: D004220:Disulfides; D047392:beta-Cyclodextrins; D013213:Starch; D005087:Glucan 1,4-alpha-Glucosidase