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Thermal stability and atomic-resolution crystal structure of the Bacillus caldolyticus cold shock protein

Item Type:Article
Title:Thermal stability and atomic-resolution crystal structure of the Bacillus caldolyticus cold shock protein
Creators Name:Mueller, U., Perl, D., Schmid, F.X. and Heinemann, U.
Abstract:The bacterial cold shock proteins are small compact {beta}-barrel proteins without disulfide bonds, cis-proline residues or tightly bound cofactors. Bc-Csp, the cold shock protein from the thermophile Bacillus caldolyticus shows a twofold increase in the free energy of stabilization relative to its homolog Bs-CspB from the mesophile Bacillus subtilis, although the two proteins differ by only 12 out of 67 amino acid residues. This pair of cold shock proteins thus represents a good system to study the atomic determinants of protein thermostability. Bs-CspB and Bc-Csp both unfold reversibly in cooperative transitions with T(M) values of 49.0°C and 77.3°C, respectively, at pH 7.0. Addition of 0.5 M salt stabilizes Bs-CspB but destabilizes Bc-Csp. To understand these differences at the structural level, the crystal structure of Bc-Csp was determined at 1.17 {angstrom} resolution and refined to R = 12.5% (R(free)= 17.9%). The molecular structures of Bc-Csp and Bs-CspB are virtually identical in the central {beta}-sheet and in the binding region for nucleic acids. Significant differences are found in the distribution of surface charges including a sodium ion binding site present in Bc-Csp, which was not observed in the crystal structure of the Bs-CspB. Electrostatic interactions are overall favorable for Bc-Csp, but unfavorable for Bs-CspB. They provide the major source for the increased thermostability of Bc-Csp. This can be explained based on the atomic-resolution crystal structure of Bc-Csp. It identifies a number of potentially stabilizing ionic interactions including a cation-binding site and reveals significant changes in the electrostatic surface potential.
Keywords:Atomic-Resolution Crystal Structure, Bacillus Caldolyticus, Cold Shock Protein, Electrostatic Interactions, Thermal Stability
Source:Journal of Molecular Biology
Page Range:975-988
Date:7 April 2000
PubMed:View item in PubMed

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