IbpB thermometer explained
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.
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.
Notes and References
- Gaubig LC, Waldminghaus T, Narberhaus F . Multiple layers of control govern expression of the Escherichia coli ibpAB heat-shock operon . Microbiology . 157 . Pt 1 . 66–76 . January 2011 . 20864473 . 10.1099/mic.0.043802-0 . free .
- Richmond CS, Glasner JD, Mau R, Jin H, Blattner FR . Genome-wide expression profiling in Escherichia coli K–12 . Nucleic Acids Research . 27 . 19 . 3821–3835 . October 1999 . 10481021 . 148645 . 10.1093/nar/27.19.3821 .
- Waldminghaus T, Gaubig LC, Klinkert B, Narberhaus F . The Escherichia coli ibpA thermometer is stable and unstable structural elements . RNA Biology . 6 . 4 . 455–463 . Sep–Oct 2009 . 19535917 . 10.4161/rna.6.4.9014 . free .
- Waldminghaus T, Fippinger A, Alfsmann J, Narberhaus F . RNA thermometers are common in alpha- and gamma-proteobacteria . Biological Chemistry . 386 . 12 . 1279–1286 . December 2005 . 16336122 . 10.1515/BC.2005.145 .
- Ratajczak E, Strózecka J, Matuszewska M, Zietkiewicz S, Kuczyńska-Wiśnik D, Laskowska E, Liberek K . IbpA the small heat shock protein from Escherichia coli forms fibrils in the absence of its cochaperone IbpB . FEBS Letters . 584 . 11 . 2253–2257 . June 2010 . 20433838 . 10.1016/j.febslet.2010.04.060 . free .
- Shearstone JR, Baneyx F . Biochemical characterization of the small heat shock protein IbpB from Escherichia coli . The Journal of Biological Chemistry . 274 . 15 . 9937–9945 . April 1999 . 10187768 . 10.1074/jbc.274.15.9937 . free .
- Jiao W, Hong W, Li P, Sun S, Ma J, Qian M, Hu M, Chang Z . 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 . February 2008 . 17995456 . 10.1042/BJ20071120 .
- Jiao W, Qian M, Li P, Zhao L, Chang Z . 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 . April 2005 . 15769476 . 10.1016/j.jmb.2005.01.029 .