The IbpB thermometer is an RNA thermometer element found in the ibpABoperon.[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]
^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. PMID16336122.
^ abJiao 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. PMID17995456.
^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. PMID15769476.
