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#bacterial stress response

3 public questions tagged with this topic.

Microbial Physiology

The DnaK/DnaJ/GrpE chaperone system is responsible for:

Hsp70 chaperone system DnaK-DnaJ-GrpE is highly conserved ATP-dependent folding machine from bacteria to humans. DnaK N-terminal ATPase domain linked to substrate-binding domain exists in ATP-bound low-affinity open state with rapid substrate exchange. DnaJ Hsp40 cochaperone with J-domain delivers unfolded proteins exposing hydrophobic patches and potently stimulates ATP hydrolysis via HPD motif interaction, converting DnaK to ADP-bound high-affinity closed state that tightly clamps onto extended segment of about seven residues enriched in leucine and isoleucine. GrpE dimeric nucleotide exchange factor binds DnaK and catalyzes ADP release allowing ATP rebinding and substrate discharge for another cycle or transfer to GroEL-ES chaperonin. During heat shock aggregated proteins accumulate; this machinery collaborates with ClpB disaggregase that threads aggregates through central pore, prevents irreversible inclusion bodies, resolubilizes existing foci and maintains proteome integrity. It does not catalyze DNA replication, membrane phospholipid synthesis or quorum sensing, but exclusively manages protein quality control under thermodynamic stress ensuring post-stress recovery.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 7: DnaK-DnaJ-GrpE Chaperone System in Protein Refolding.

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Microbial Physiology

Which bacterial stress response is activated in acidic environments?

Acid tolerance is vital survival strategy for enteric bacteria such as Escherichia coli, Salmonella Typhimurium and Shigella flexneri that must traverse gastric compartment where pH can fall to 1-3 and organic acid stress in intestine. Enterobacteriaceae deploy multiple amino acid decarboxylase antiporter systems for pH homeostasis. Under acidic conditions, inducible decarboxylases such as CadA lysine decarboxylase, AdiA arginine decarboxylase and GadA/B glutamate decarboxylases consume an intracellular proton during decarboxylation of substrate to produce cadaverine, agmatine and gamma-aminobutyrate respectively plus CO2. The more alkaline product is exported via specific antiporters CadB, AdiC and GadC in 1:1 exchange for fresh extracellular substrate, effectively exporting proton equivalents and raising internal pH by up to 0.5 units. CadB-dependent lysine decarboxylation generates cadaverine that additionally blocks outer membrane porins OmpF and OmpC to reduce proton leak. This system raises membrane potential, maintains enzyme function and prevents DNA damage. PhoP-PhoQ senses Mg2+ limitation and antimicrobial peptides, OxyR senses peroxide, SoxR senses superoxide, so acid-specific decarboxylation antiporter module represents the major pH homeostasis strategy underpinning enteric pathogenesis.

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Acid Stress Response and CadB Decarboxylase System.

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Gene regulation in Prokaryotes

Alternative sigma factor σ32 is involved in

Alternative sigma factors redirect RNA polymerase holoenzyme to distinct promoter classes under stress conditions. Sigma32 encoded by rpoH in Escherichia coli accumulates during temperature upshift because heat-induced misfolded proteins titrate chaperones DnaK, DnaJ, GroEL, releasing sigma32 from sequestration and from FtsH-mediated proteolysis. Free sigma32 binds core polymerase, activating heat-shock promoters defined by -35 CTTGAA and -10 CCCCATNT consensus driving transcription of chaperones GroEL, DnaK, proteases ClpB, Lon, and repair proteins. This rapid reprogramming restores proteostasis, increases refolding capacity, and provides transient thermotolerance until homeostasis returns and sigma32 degraded via feedback regulation.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8: Heat Shock Sigma Factor σ32 Regulation

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