title: Dunaliella salina Hsp90 is halotolerant.
abstract: Dunaliella salina is a unicellular green alga with exceptional halotolerance. Although the D. salina cells are capable to proliferate in hypersaline medium, the intracellular salt concentrations are maintained at a low level. Thus the extracellular but not intracellular Dunaliella proteins are expected to be highly halotolerant. In this research, we compared the salt-dependence of the activity and stability of Hsp90s from the halotolerant alga D. salina (dsHsp90) and the mesophilic alga Chlamydomonas reinhardtii (crHsp90). We found that the ATPase activity of crHsp90 could be enhanced about six-fold by 2M NaCl, while the activity of dsHsp90 showed a much weaker dependence on salinity. When denatured by urea, both crHsp90 and dsHsp90 exhibited an apparent three-state unfolding with the population of an unfolding intermediate. High salinity significantly decreased the Gibbs free energy change of crHsp90 but not dsHsp90 for the transition from the native state to the intermediate. The little dependence of dsHsp90 activity and folding on salinity suggests that dsHsp90 is halotolerant though it is an intracellular protein. We propose that the halotolerance of intracellular Dunaliella proteins might play a role in fighting against the transient intracellular salt fluctuations during hyperosmotic or hypoosmotic shock.
authors: Key Laboratory of Bio-Resources and Eco-Environment of MOE, College of Life Science, Sichuan University, Chengdu 610064, China; State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Xiang-Jun
authors: XJ
authors: Chen
authors: Key Laboratory of Bio-Resources and Eco-Environment of MOE, College of Life Science, Sichuan University, Chengdu 610064, China; State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Ming-Jie
authors: MJ
authors: Wu
authors: Key Laboratory of Bio-Resources and Eco-Environment of MOE, College of Life Science, Sichuan University, Chengdu 610064, China.
authors: Yan
authors: Y
authors: Jiang
authors: Key Laboratory of Bio-Resources and Eco-Environment of MOE, College of Life Science, Sichuan University, Chengdu 610064, China. Electronic address: yangyi528@scu.edu.cn.
authors: Yi
authors: Y
authors: Yang
authors: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China. Electronic address: ybyan@tsinghua.edu.cn.
authors: Yong-Bin
authors: YB
authors: Yan
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D000595:Amino Acid Sequence; D002696:Chlamydomonas / Q000187:drug effects / Q000378:metabolism; D000460:Chlorophyta / Q000187:drug effects / Q000378:metabolism*; D002850:Chromatography, Gel; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D058767:Protein Unfolding / Q000187:drug effects; D054712:Salinity; D012965:Sodium Chloride / Q000494:pharmacology; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology
chemical_list: D018841:HSP90 Heat-Shock Proteins; D012965:Sodium Chloride; D014508:Urea
keywords: Halotolerance; Protein folding; Structural stability