title: Strategy for cold adaptation of the tryptophan synthase α subunit from the psychrophile Shewanella frigidimarina K14-2: crystal structure and physicochemical properties.
abstract: To investigate the molecular basis of cold adaptation of enzymes, we determined the crystal structure of the tryptophan synthase α subunit (SfTSA) from the psychrophile Shewanella frigidimarina K14-2 by X-ray analysis at 2.6-Å resolution and also examined its physicochemical properties. SfTSA was found to have the following characteristics: (i) The stabilities against heat and denaturant of SfTSA were lower than those of an α subunit (EcTSA) from Escherichia coli. This lower equilibrium stability originated from both a faster unfolding rate and a slower refolding rate; (ii) the heat denaturation of SfTSA was completely reversible at pH 7.0 and the solubility of denatured SfTSA was higher than that of denatured EcTSA. The two-state transition of denaturation for SfTSA was highly cooperative, whereas the denaturation process of EcTSA was considerably more complex and (iii) the global structure of SfTSA was quite similar to those of α subunits from other species. Relative to those other proteins, SfTSA exhibited an increase in cavity volume and a decrease in the number of ion pairs. SfTSA also lacks a hydrogen bond near loop B, related to catalytic function. These characteristics of SfTSA might provide the conformational flexibility required for catalytic activity at low temperatures.
authors.affiliation: Department of Ocean Sciences, Graduate school of Marine Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7, Konan, Minato, Tokyo 108-8477; Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871; Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871; Department of Biomolecular Chemistry, Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto 606-8522; Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871; Department of Life Science, University of Hyogo, 3-2-1, Kouto, Kamigori, Ako-gun, Hyogo 678-1297; and RIKEN SPring-8 Center, RIKEN Harima Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Mitsuya
authors.forename: Shun-ichi
authors.initials: S
authors.lastname: Tanaka
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Matsumura
authors.forename: Naoto
authors.initials: N
authors.lastname: Urano
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Takano
authors.forename: Kyoko
authors.initials: K
authors.lastname: Ogasahara
authors.forename: Michiyo
authors.initials: M
authors.lastname: Takehira
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Yutani
authors.forename: Masami
authors.initials: M
authors.lastname: Ishida
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D002152:Calorimetry, Differential Scanning; D003080:Cold Temperature; D018360:Crystallography, X-Ray; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D008968:Molecular Conformation; D011489:Protein Denaturation; D016415:Sequence Alignment; D020592:Shewanella / Q000737:chemistry* / Q000201:enzymology*; D014367:Tryptophan Synthase / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D014367:Tryptophan Synthase
keywords: cold adaptation; crystal structure; protein unfolding and refolding; psychrophile; tryptophan synthase α subunit