Entropic stabilization of the tryptophan synthase α-subunit from a hyperthermophile, Pyrococcus furiosus : X-ray analysis and calorimetry

This research was originally published in Journal of Biological Chemistry. Yuriko Yamagata, Kyoko Ogasahara, Yusaku Hioki, Soo Jae Lee, Atsushi Nakagawa, Haruki Nakamura, Masami Ishida, Seiki Kuramitsui, and Katsuhide Yutani. Entropic stabilization of the tryptophan synthase α-subunit from a hyperthermophile, Pyrococcus furiosus : X-ray analysis and calorimetry. J. Biol. Chem. 2001; 276, 11062-11071. © the American Society for Biochemistry and Molecular Biology

Effect of heavy atoms on the thermal stability of α-amylase from Aspergillus oryzae.

Currently, there are no versatile and established methods for improving stability of proteins. In an entirely different approach from conventional techniques such as mutagenesis, we attempted to enhance enzyme stability of α-amylase from Aspergillus oryzae using a heavy-atom derivatization technique. We evaluated changes in stability using differential scanning calorimetry (DSC). Candidate heavy atoms were identified using the Heavy-Atom Database System HATODAS, a Web-based tool designed to assist in heavy-atom derivatization of proteins for X-ray crystallography. The denaturation temperature of α-amylase derivatized with gadolinium (Gd) or samarium (Sm) ions increased by 6.2 or 5.7°C, respectively, compared to that of the native protein (60.6°C). The binding of six Gd ions was confirmed by X-ray crystallography of the enzyme at 1.5 Å resolution. DSC and dynamic light-scattering data revealed a correlation between stability and the aggregation state upon addition of Gd ions. These results show that HATODAS search is an effective tool for selecting heavy atoms for stabilization of this protein

Absence of the thermal transition in apo-α-lactalbumin in the molten globule state : A study by differential scanning microcalorimetry

To estimate the energy level of the molten globule state, the heat capacity function of apo-α-lactalbumin in the molten globule state has been examined using a scanning microcalorimeter at neutral pH. The results showed that the enthalpy difference between the molten globule state and presumed unfolded state by heating was almost zero at neutral pH, demonstrating that the molten globule state does not exhibit any co-operative transition upon heating. This is in agreement with the results already reported at acid pH, but is apparently in conflict with that recently reported with some assumptions at neutral pH