title: Thermodynamic and kinetic determinants of Thermotoga maritima cold shock protein stability: a structural and dynamic analysis.
abstract: The cold shock protein (CSP) from hyperthermophile Thermotoga maritima (TmCSP) is only marginally stable (DeltaG(T(opt)) = 0.3 kcal/mol) at 353 K, the optimum environmental temperature (T(opt)) for T. maritima. In comparison, homologous CSPs from E. coli (DeltaG(T(opt)) = 2.2 kcal/mol) and B. subtilis (DeltaG(T(opt)) = 1.5 kcal/mol) are at least five times more stable at 310 K, the T(opt) for the mesophiles. Yet at the room temperature, TmCSP is more stable (DeltaG(T(R)) = 4.7 kcal/mol) than its homologues (DeltaG(T(R)) = 3.0 kcal/mol for E. coli CSP and DeltaG(T(R)) = 2.1 kcal/mol for B. subtilis CSP). This unique observation suggests that kinetic, rather than thermodynamic, barriers toward unfolding might help TmCSP native structure at high temperatures. Consistently, the unfolding rate of TmCSP is considerably slower than its homologues. High temperature (600 K) complete unfolding molecular dynamics (MD) simulations of TmCSP support our hypothesis and reveal an unfolding scheme unique to TmCSP. For all the studied homologues of TmCSP, the unfolding process first starts at the C-terminal region and N-terminal region unfolds in the end. But for TmCSP, both the terminals resist unfolding for consistently longer simulation times and, in the end, unfold simultaneously. In TmCSP, the C-terminal region is better fortified and has better interactions with the N-terminal region due to the charged residues, R2, E47, E49, H61, K63, and E66, being in spatial vicinity. The electrostatic interactions among these residues are unique to TmCSP. Consistently, the room temperature MD simulations show that TmCSP is more rigid at its N- and C-termini as compared to its homologues from E. coli, B. subtilis, and B. caldolyticus.
authors.affiliation: Computational Biology Research Center (CBRC), National Institute of Advanced Industrial Science and Technology (AIST), AIST Tokyo Waterfront Bio-IT Research Building, Koto-ku, Tokyo 135-0064, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Motono
authors.forename: M Michael
authors.initials: MM
authors.lastname: Gromiha
authors.forename: Sandeep
authors.initials: S
authors.lastname: Kumar
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry; D003080:Cold Temperature; D003198:Computer Simulation; D029968:Escherichia coli Proteins / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008969:Molecular Sequence Data; D016601:RNA-Binding Proteins; D016415:Sequence Alignment; D013816:Thermodynamics; D020124:Thermotoga maritima / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C491179:CspB protein, E coli; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D016601:RNA-Binding Proteins; C407094:cold shock protein, Bacillus