title: Stabilization mechanism of the tryptophan synthase alpha-subunit from Thermus thermophilus HB8: X-ray crystallographic analysis and calorimetry.
abstract: In order to elucidate the thermo-stabilization mechanism of the tryptophan synthase alpha-subunit from the extreme thermophile Thermus thermophilus HB8 (Tt-alpha-subunit), its crystal structure was determined and its stability was examined using DSC. The results were compared to those of other orthologs from mesophilic and hyperthermophilic organisms. The denaturation temperature of the Tt-alpha-subunit was higher than that of the alpha-subunit from S. typhimurium (St-alpha-subunit) but lower than that of the alpha-subunit from P. furiosus (Pf-alpha-subunit). Specific denaturation enthalpy and specific denaturation heat capacity values of the Tt-alpha-subunit were the lowest among the three proteins, suggesting that entropy effects are responsible for the stabilization of the Tt-alpha-subunit. Based on a structural comparison with the St-alpha-subunit, two deletions in loop regions, an increase in the number of ion pairs and a decrease in cavity volume seem to be responsible for the stabilization of the Tt-alpha-subunit. The results of structural comparison suggest that the native structure of the Tt-alpha-subunit is better adapted to an ideally stable structure than that of the St-alpha-subunit, but worse than that of the Pf-alpha-subunit. The results of calorimetry suggest that the residual structure of the Tt-alpha-subunit in the denatured state contributes to the stabilization.
authors.affiliation: Advanced Protein Crystallography Research Group, RIKEN Harima Institute at SPring-8, 1-1-1 Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5148.
authors.forename: Yukuhiko
authors.initials: Y
authors.lastname: Asada
authors.forename: Masahide
authors.initials: M
authors.lastname: Sawano
authors.forename: Kyoko
authors.initials: K
authors.lastname: Ogasahara
authors.forename: Junji
authors.initials: J
authors.lastname: Nakamura
authors.forename: Motonori
authors.initials: M
authors.lastname: Ota
authors.forename: Chizu
authors.initials: C
authors.lastname: Kuroishi
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Sugahara
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Yutani
authors.forename: Naoki
authors.initials: N
authors.lastname: Kunishima
mesh_terms: D000595:Amino Acid Sequence; D002151:Calorimetry; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D013696:Temperature; D016963:Thermus thermophilus / Q000201:enzymology*; D014367:Tryptophan Synthase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D014367:Tryptophan Synthase