IbpB thermometer
Conserved secondary structure of the IbpB thermometer
Identifiers
SymbolibpB 5' UTR
Other data
RNA typeRNA thermometer
Domain(s)E. coli
PDB structuresPDBe

The IbpB thermometer is an RNA thermometer element found in the ibpAB operon.[1] The operon contains two heat-shock genes, encoding inclusion body binding proteins A and B (IbpA/B), and is the most drastically upregulated operon under heat-shock in Escherichia coli.[2]

IbpA is regulated by a ROSE element found in its 5' UTR,[3][4] while IbpB has its own heat-sensitive cis-regulatory element. The activity of this thermoregulator was confirmed in vitro but was not found in vivo, suggesting more complicated operon regulation exists in bacterial cells.[1]

IbpB protein

The IbpB protein, whose expression is regulated by the IbpB thermometer, is 48% identical to IbpA (at the level of amino acid sequence) yet fulfils a different role in heat shock. When IbpB is absent, IbpA protein will form long fibrils which is unusual for a heat shock protein; IbpB, acting as a co-chaperone, inhibits IbpA from forming this structure.[5]

Under heat shock, IbpB protein dissociates to give two smaller subunits and also rearranges its tertiary structure.[6] This "remarkable conformational transformation"[7] is thought to be essential for IbpB to act as a co-chaperone with IbpA under heat shock.[8]

IbpB has been found to retain active for a significant time after a heat shock stimulus has been removed.[7]

References

  1. 1 2 Gaubig LC, Waldminghaus T, Narberhaus F (January 2011). "Multiple layers of control govern expression of the Escherichia coli ibpAB heat-shock operon". Microbiology. 157 (Pt 1): 66–76. doi:10.1099/mic.0.043802-0. PMID 20864473.
  2. ↑ Richmond CS, Glasner JD, Mau R, Jin H, Blattner FR (October 1999). "Genome-wide expression profiling in Escherichia coli K–12". Nucleic Acids Research. 27 (19): 3821–3835. doi:10.1093/nar/27.19.3821. PMC 148645. PMID 10481021.
  3. ↑ Waldminghaus T, Gaubig LC, Klinkert B, Narberhaus F (Sep–Oct 2009). "The Escherichia coli ibpA thermometer is comprised of stable and unstable structural elements". RNA Biology. 6 (4): 455–463. doi:10.4161/rna.6.4.9014. PMID 19535917.
  4. ↑ Waldminghaus T, Fippinger A, Alfsmann J, Narberhaus F (December 2005). "RNA thermometers are common in alpha- and gamma-proteobacteria". Biological Chemistry. 386 (12): 1279–1286. doi:10.1515/BC.2005.145. PMID 16336122.
  5. ↑ Ratajczak E, Strózecka J, Matuszewska M, Zietkiewicz S, Kuczyńska-Wiśnik D, Laskowska E, Liberek K (June 2010). "IbpA the small heat shock protein from Escherichia coli forms fibrils in the absence of its cochaperone IbpB". FEBS Letters. 584 (11): 2253–2257. doi:10.1016/j.febslet.2010.04.060. PMID 20433838.
  6. ↑ Shearstone JR, Baneyx F (April 1999). "Biochemical characterization of the small heat shock protein IbpB from Escherichia coli". The Journal of Biological Chemistry. 274 (15): 9937–9945. doi:10.1074/jbc.274.15.9937. PMID 10187768.
  7. 1 2 Jiao W, Hong W, Li P, Sun S, Ma J, Qian M, Hu M, Chang Z (February 2008). "The dramatically increased chaperone activity of small heat-shock protein IbpB is retained for an extended period of time after the stress condition is removed". The Biochemical Journal. 410 (1): 63–70. doi:10.1042/BJ20071120. PMID 17995456.
  8. ↑ Jiao W, Qian M, Li P, Zhao L, Chang Z (April 2005). "The essential role of the flexible termini in the temperature-responsiveness of the oligomeric state and chaperone-like activity for the polydisperse small heat shock protein IbpB from Escherichia coli". Journal of Molecular Biology. 347 (4): 871–884. doi:10.1016/j.jmb.2005.01.029. PMID 15769476.
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