title: Without salt, the 'thermophilic' protein Mth10b is just mesophilic.
abstract: Most proteins from thermophiles or hyperthermophiles are intrinsically thermostable. However, though Methanobacterium thermoautotrophicum ΔH is a thermophilic archaeon with an optimal growth temperature of 65 °C, Mth10b, an atypical member the Sac10b protein family from M. thermoautotrophicum ΔH, seems not intrinsically thermostable. In this work, to clarify the molecular mechanism of Mth10b remaining stable under its physiological conditions, the thermodynamic properties of Mth10b were studied through equilibrium unfolding experiments performed at pH 7.0 monitored by circular dichroism (CD) spectra in detail. Our work demonstrated that Mth10b is not intrinsically thermostable and that due to the masking effect upon the large numbers of destabilizing electrostatic repulsions resulting from the extremely uneven distribution of charged residues over the surface of Mth10b, salt can contribute to the thermostability of Mth10b greatly. Considering that the intracellular salt concentration is high to 0.7 M, we concluded that salt is the key extrinsic factor to Mth10b remaining stable under its physiological conditions. In other word, without salt, 'thermophilic' protein Mth10b is just a mesophilic one.
authors.affiliation: Ministry of Education Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Nan
authors.initials: N
authors.lastname: Zhang
authors.forename: Xian-Ming
authors.initials: XM
authors.lastname: Pan
authors.forename: Meng
authors.initials: M
authors.lastname: Ge
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli; D006358:Hot Temperature; D017014:Methanobacterium; D011487:Protein Conformation; D017510:Protein Folding; D012965:Sodium Chloride
chemical_list: D001426:Bacterial Proteins; D012965:Sodium Chloride