ABSTRACT
Parallel with the heat/light-induced thylakoid microdomain reorganization and thermal stabilization of photosynthesis we observed an increase in the level of the highly saturated monoglucosyldiacylglycerol (MGlcDG) in Synechocystis cells. The unusually high microviscosity obtained in thylakoid MGlcDG liposomes by monitoring DPH anisotropy was in good agreement with its exceptionally high acyl chain saturation. The MGlcDG membranes remained stable even at extreme high temperatures. Strikingly, in monolayer experiments, out of the five thylakoid polar lipids tested, MGlcDG expressed the strongest interaction with the thylakoid-stabilizing small Hsp from Synechocystis, Hsp17. The preferential interaction of Hsp17 with non-bilayer phase forming lipids supports our notion that sHsps counteract the formation of thermally induced local non-bilayer structures [Proc. Natl. Acad. Sci. USA 99 (2002) 13504] and thus implicated in microdomain organization and in the preservation of functional integrity of thylakoid membranes challenged by heat stress in the light. We also suggest that the highly saturated MGlcDG functions as a "heat shock lipid" and is of potential importance in the development of acquired thermotolerance of heat/light-primed cyanobacterial thylakoids.
Subject(s)
Cyanobacteria/metabolism , Anisotropy , Cell Membrane/metabolism , Chromatography, Liquid , Fatty Acids/chemistry , Heat-Shock Proteins/chemistry , Heat-Shock Proteins/metabolism , Hot Temperature , Light , Lipid Bilayers/chemistry , Lipids/chemistry , Liposomes/metabolism , Mass Spectrometry , Models, Chemical , Molecular Chaperones/metabolism , Photosynthesis , Protein Binding , Protein Structure, Tertiary , Synechocystis , Temperature , Thylakoids/metabolism , Time FactorsABSTRACT
Treatment of Escherichia coli with non-lethal doses of heat or benzyl alcohol (BA) causes transient membrane fluidization and permeabilization, and induces the rapid transcription of heat-shock genes in a sigma32-dependent manner. This early response is followed by a rapid adaptation (priming) of the cells to otherwise lethal elevated temperature, in strong correlation with an observed remodeling of the composition and alkyl chain unsaturation of membrane lipids. The acquisition of cellular thermotolerance in BA-primed cells is unrelated to protein denaturation and is not accompanied by the formation of major heat-shock proteins, such as GroEL and DnaK. This suggests that the rapid remodeling of membrane composition is sufficient for the short-term bacterial thermotolerance.
Subject(s)
Escherichia coli/physiology , Escherichia coli/radiation effects , Heat-Shock Response/physiology , Heat-Shock Response/radiation effects , Hot Temperature , Membrane Fluidity/physiology , Membrane Fluidity/radiation effects , Adaptation, Physiological/drug effects , Adaptation, Physiological/physiology , Adaptation, Physiological/radiation effects , Benzyl Alcohol/pharmacology , Cell Membrane Permeability/drug effects , Cell Membrane Permeability/physiology , Cell Membrane Permeability/radiation effects , Dose-Response Relationship, Drug , Dose-Response Relationship, Radiation , Escherichia coli/drug effects , Escherichia coli/ultrastructure , Heat-Shock Response/drug effects , Membrane Fluidity/drug effectsABSTRACT
We examined the expression and the function of the DnaK chaperone family in the photoautotrophic cyanobacterium, Synechocystis PCC 6803. Surprisingly, only one of the three dnaK genes was transcribed either under normal or heat shock conditions. Their predicted cochaperones (four dnaJs and one grpE) proved to be uninducible under our experimental conditions. Attempts to inactivate the active dnaK2 has failed, indicating that the gene is essential. The partial mutant displayed lower inducibility of chaperones (especially GroEL and HSP17) both at mRNA and protein levels upon heat shock. The mutant showed temperature sensitive phenotype, but was able to acquire thermotolerance.
Subject(s)
Cyanobacteria/metabolism , HSP70 Heat-Shock Proteins/biosynthesis , HSP70 Heat-Shock Proteins/physiology , Bacterial Proteins/biosynthesis , Bacterial Proteins/genetics , Cyanobacteria/genetics , Cyanobacteria/growth & development , Gene Expression Regulation, Bacterial , Genes, Bacterial , HSP40 Heat-Shock Proteins , HSP70 Heat-Shock Proteins/genetics , Heat-Shock Proteins/biosynthesis , Heat-Shock Proteins/genetics , Heat-Shock Response , Multigene Family , Mutation , Photosynthesis , RNA, Bacterial/biosynthesis , Transcription, GeneticABSTRACT
Thermal stress in living cells produces multiple changes that ultimately affect membrane structure and function. We report that two members of the family of small heat-shock proteins (sHsp) (alpha-crystallin and Synechocystis HSP17) have stabilizing effects on model membranes formed of synthetic and cyanobacterial lipids. In anionic membranes of dimyristoylphosphatidylglycerol and dimyristoylphosphatidylserine, both HSP17 and alpha-crystallin strongly stabilize the liquid-crystalline state. Evidence from infrared spectroscopy indicates that lipid/sHsp interactions are mediated by the polar headgroup region and that the proteins strongly affect the hydrophobic core. In membranes composed of the nonbilayer lipid dielaidoylphosphatidylethanolamine, both HSP17 and alpha-crystallin inhibit the formation of inverted hexagonal structure and stabilize the bilayer liquid-crystalline state, suggesting that sHsps can modulate membrane lipid polymorphism. In membranes composed of monogalactosyldiacylglycerol and phosphatidylglycerol (both enriched with unsaturated fatty acids) isolated from Synechocystis thylakoids, HSP17 and alpha-crystallin increase the molecular order in the fluid-like state. The data show that the nature of sHsp/membrane interactions depends on the lipid composition and extent of lipid unsaturation, and that sHsps can regulate membrane fluidity. We infer from these results that the association between sHsps and membranes may constitute a general mechanism that preserves membrane integrity during thermal fluctuations.
