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HEAT SHOCK RESPONSE

IN BACTERIAL CELL

HEAT SHOCK RESPONSE

IN BACTERIAL CELL

PRESENTED BYSHALINI SAINIM.Sc.2ND SEMROLL NO.1810

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CONTENTSCONTENTS

• Gneral stress for bacteria• Strategies to fight from the stress• Examples of stress in bacteria1. Specific stress responses2. General stress responses• Regulation principle of heat shock response in E.coli• Outline of heat shock reponse• rpoH mRNA as thermometer• Heat shock response in E.coli • The Hsps of E.coli• Modulation of heat shock response• Role of σ32,DnaJ/DnaK, and RNAP• At the level of adaptation• Regulation • References

3Molbio.com

GENERAL INTRODUCTION

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1.Physiolochemical and chemical parameters Pressure, temperature, turgor pressure, irradiation, pH,osmolite/salt

Concentration , oxygen, redox-state.

2.Nutritional DeprivationStravation of nutients (carbon, phosphate, nitrogen, amino acids,andwater) 3.Toxic compoundsToxins, antibiotics, heavy metals, mutagens 4.Interaction with other cellsHosts cells during infections, high cell density

STRESS FOR BACTERIASTRESS FOR BACTERIA

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STRATEGIES TO FIGHT THE EFFECT OF STRESSSTRATEGIES TO FIGHT THE EFFECT OF STRESS

1. Elimination of stress factorsAdjustment of intracellular osmolarity Destruction or secretion of toxins compounds searches for

nutritions etc.

2. Repair and damageDNA repairProtein repair etc.

2. Escape from the stress situation Chemotactic movement towards attractants/away from the repellent Formation of spores and capsules Morphological adaptations through differntiationDevelopment of resistance

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EXAMPLES OF BACTERIAL STRESS RESPONSES

EXAMPLES OF BACTERIAL STRESS RESPONSES

1. Specific stress responses• Heat shock• Cold shock• Envelope stress• Oxidation stress• Oxygen deprivation• Amino acid starvation • Osmotic stress• Acid stress• Sodium stress• SOS response to DNA damage (UV light)• Metalloregulation between bacterial metals

haemostatis and resistance

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•Adaptive mutation

•Sporulation

•Long term survival in the stationary phase

General stress ResponsesGeneral stress Responses

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REGULATION PRINCIPLE OF THE HEAT SHOCK RESPONSE IN

E.coli

REGULATION PRINCIPLE OF THE HEAT SHOCK RESPONSE IN

E.coli

Alternate sigma factor :Sigma 32

Levels of regulation:

Transcription TranslationProtein activityProtein stability

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Outline of heat shock response

Outline of heat shock response

Pics-sciencedaily.com

Conformation change of HSF duringNormal to heat stimulus conditions

10Bakau-heat Shock response

mRNAHeat melts the tertiary structure

-shine dalgarno-seqget free

Translation is facilitated

(gene encoded by rpoH)-act as a messe--nger.

mRNA TRANSCRIPT

mRNA

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HEAT SHOCK RESPONSE IN E.coli HEAT SHOCK RESPONSE IN E.coli

• In this organisms there are two heat shock regulons both of which are positivly regulated at the level of transcription by an

alternate σ- factor. The major one is regulated by σ-32(σ-H) and the minor one is regulated by σ-24.

• Upon from shift from 30°C to 40°C, E.coli and other bacteria transiently increases the rate of synthesis of a set of proteins called heat shock proteins (HSPs).

• Many of the HSPs are required for the cell. Many of these HSPs are required for the cell growth or survival at more elevated temperatures (thermtolerance) for thermophiles.

• Among the induced proteins are DnaJ and DnaK, the RNA polymerase σ70 subunit lon, ClpAP, FtsH, LysU(protease). There are nearly 50 heat shock poteins identified in E.coli.

12Bakau- heat shock Reponse in E.coli

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• The σH regulon provides protection against cytoplasmic thermal stress. The E.coli rpoH locus encodes a 32kD σ factor, alternativly called σ H or σ32 , which redirects promotor specificity of RNA polymerase(RNAP). The σ32 protein regulates the expression of 34 heat shock genes.

• The simple explanation for how heat shock increases expression of the σ32 regulon ,is that heat shock first cause in elevation in σ32 levels, which in turn increases expression of the σ32 target genes.

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MODULATION OF HEAT SHOCK

RESPONSE IN E.coli

MODULATION OF HEAT SHOCK

RESPONSE IN E.coli

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Sigma-70rpoH

42°C

Sigma-32

DnaJ

GrpE

Dnak

Sigma-32

GrpEDnaK DnaJ

30°C

Inactive, unstable,degradedFtsH,HsIUV,ClpAP,Protease

mRNA

Translation

Sigma-32

βα

βαSigma-32

HEAT SHOCKGENES

30°C

Dnak DnaJ LysU GroE GrpE etc.

CHAPRONINEFUNCTIONS

Nativeprotein

UV

pH

H2O2

Dnak DnaJGrpE

COMPLEX

Unfolded protein

42°C

Flow chart From

Moat andfroaster

House-Keeping σ factor

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•First temperature upshift from 30°C to 42°C results in the increased translation of rpoH message.

•Cis- acting mRNA sites within the 5′ region of rpoH message form temperature -sensitive secondary structures that sequester the ribosomes binding site. •At high temperature these secondary structures melt, thereby enabling more efficient translation of the rpoH message.

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• In addition to the increased translation of rpoH message, the σ32 protein itself become more stable, at least transiently. The mechanism regulating proteolysis centers on wether σ32 associates with RNA polymerase.

• During growth at 30°C,σ32 can be degraded by several proteases including FtsH,HsIVU, and ClpAP. However , if σ32 is bound to RNAP, σ32 is protected from degradation.

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•The cell use DnaK-DnaJ-GrpE chaperone team to interact with σ32 at low temperature, sequestering σ32 from RNA polymerase.

•Upon heat shock, there is an increase in the number of other unfolded proteins or denatured proteins that can be bind to DnaK/DnaJ molecules available to bind σ 32, allowing σ32 to bind with RNAP, which protects σ 32 from degradation.

ROLE OF σ32 ,DnaK/DnaJ AND RNAPROLE OF σ32 ,DnaK/DnaJ AND RNAP

Pic-sciencedirect.com

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AT THE LEVEL OF THE ADAPTATION

AT THE LEVEL OF THE ADAPTATION

• As the cell reaches the adaptation phase following heat shock, the level of the DnaK and DnaJ rise and can again bind σ32, redirecting it toward degradation.

• Nevertheless, even through σ 32 degradation resumes, translation of rpoH remains high at the evaluated temperature and σ32 continues to accumulate, although at a slower rate.

• In addition of translational and protelytic controls, production of σ 32 in regulated at the transcriptional level via a feedback mechanism.

• There are four promoters driving rpoH expression, three of which are dependent on σ 70, the housekeeping σ factor.

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• They seemly diverse stresses activate rpoH that

appears responsible is the accumulation of denatured or incomplete peptides.

• There is a potential alarmone that has been implicated in signaling exepressions of this global network.

• The σE regulon provide protection against extracytoplasmic stress.

• The hallmark of the gram- Negative cell is the existence of two membrane-bound subcellular compartments:the cytoplasm and the periplasm conditions in each of these compartments differs makedly.

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Bauku molbio-heat shock response

22Microbiallife.com

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Regulatory mechanismRegulatory mechanism• Regulated by additional or alternative control channels. These

operon is coding with Hsp10+60 and Hsp70(coded Dnak& groE operons),respectively contain regulatory inverted repeat (IR=CIRCE) and trancribed by vegetative factors like σ70 and σ32 factor. Orf act as represser or HrcA represser.

• The CIRCE normally repressed by the HrcA represser but can be induced by inactivating. The molecular switch involve chaperone GroE. This is bind with represser and facilitates folding of HrcA and thereby modulate represser function.

• The IR functions at the DNA level as a represser binding site and also controls the half life of the transcripts under non heat conditions.

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References • Research article -Buakau, B.1993.regulation in E.coli heat

shock response.Mol. Microbial.• Albert G. Moat, Jhon W. Foster ,Michael P. Spector ,fourth

edition 2004 ,Microbial physiology page no. 597,598,599,600,601.

• Sciencedirect.com• Sciencedaily.com• Molbio.com• Microbiallife.com• Research papers---• Research paper-heat shock proteins molecular chaperones,and

the stress reponse-Martin E. feeder dept of organism biology and community on evolutionary biology, University of Chicago.

• Regulation of heat shock response in bacteria-Gil Segal and Elora Z. Ron dept. of molecular biology and biotechnology,Tel Aviv University Israel.

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