Thermodynamic Effects of Disulfide Bond on Thermal Unfolding of the Starch-Binding Domain ofAspergillus nigerGlucoamylase

Hayuki SUGIMOTO, Miho NAKAURA, Yoshie KOSUGE, Kunio IMAI, Hideo MIYAKE, Shuichi KARITA, Akiyoshi TANAKA
2007 Bioscience, biotechnology and biochemistry  
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 Cys-3Ser/Cys98Ser. The circular dichroism spectra and the thermodynamic parameters of binding with -cyclodextrin at 25 C suggested that the native structures of the three proteins are essentially the same. Differential scanning calorimetry
more » ... anning calorimetry of the thermal unfolding of the proteins showed that the unfolding temperature t 1=2 of the two mutant proteins decreased by about 10 C as compared to the wild-type protein at pH 7.0. At t 1=2 of the wild-type protein (52.7 C), the mutant proteins destabilized by about 10 kJ mol À1 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.
doi:10.1271/bbb.70098 pmid:17587686 fatcat:hvxok5myqvcl5lcfdrniadi7dy