title: Crystal structure of histidine-containing phosphocarrier protein from Thermoanaerobacter tengcongensis MB4 and the implications for thermostability.
abstract: Protein thermostability is an inherent characteristic of proteins from thermophilic microorganisms, and therefore enables these organisms to survive at extreme temperatures. Although it is well-known that thermostable proteins are critical for the growth of thermophilic organisms, the structural basis of protein thermostability is not yet fully understood. The histidine-containing phosphocarrier (HPr) protein, a phosphate shuttle protein in the phosphoenolpyruvate-dependent sugar transport system (PTS) of bacterial species, is an ideal model for investigating protein thermostability with respect to its small size and deficiency in disulphide bonds or cofactors. In this study, the HPr protein from Thermoanaerobacter tengcongensis (TtHPr) is cloned and purified. Crystal structure with good quality has been determined at 2.3 Å resolution, which provides a firm foundation for exploring the thermostable mechanism. However, it shows that the crystal structure is conserved and no clue can be obtained from this single structure. Furthermore, detailed comparison of sequence and structure with the homologs from meso- or thermophilic bacteria shows no obvious rule for thermostability, but the extra salt-bridge existing only in thermophilic bacteria might be a better explanation for thermostability of HPr. Thus, mutations are performed to interrupt the salt-bridge in HPrs in thermophilic bacteria. Using site-directed mutations and the circular dichroism method, thermostability is evaluated, and the mutational variations are shown to have a faster denaturing rate than for wild-type viruses, indicating that mutations cause instability in the HPrs. Understanding the higher-temperature resistance of thermophilic and hyperthermophilic proteins is essential to studies on protein folding and stability, and is critical in engineering efficient enzymes that can work at a high temperature.
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: ChunYan
authors.initials: C
authors.lastname: Feng
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: YiWei
authors.initials: Y
authors.lastname: Liu
authors.forename: GuiHua
authors.initials: G
authors.lastname: Wang
authors.forename: Hao
authors.initials: H
authors.lastname: Peng
authors.forename: YanHe
authors.initials: Y
authors.lastname: Ma
authors.forename: JingHua
authors.initials: J
authors.lastname: Yan
authors.forename: George Fu
authors.initials: GF
authors.lastname: Gao
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D016415:Sequence Alignment; D046968:Thermoanaerobacter / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr