Team:Jilin China/Background

BACKGROUND
Thermoregulation


Temperature Sensing Biological Systems

Overview

  • Sensing and responding to temperature are essential for bacterial survival

    There are always challenges for bacterial survival, especially to keep suitable living status facing fluctuations of chemical and physical parameters[1]. The common chemical perturbations include sudden deprivation of nutrients or key metabolites and changes in surrounding pH. And the most representative physical deviation is temperature shift. But in most cases, the ambient temperature change is more essential for bacterial life cycle than chemical parameters, due to the efficiency of all cellular processes is temperature dependent, especially the expression of any given gene[2,3]. Therefore, it’s indispensable for bacteria to evolve effective strategies, which can respond to temperature forwardly before the damages such as unfolded proteins or membrane rigidification occur[4].(figure 1).

  • Biological signal transduction systems that detect temperature shifts

    When it comes to the biological behavior of temperature sensing, it’s very important to elicit a proper response that could coordinate the expression of temperature-relevant genes. The common detecting systems in bacterial cells are based on three manners as following:

    1.Transcriptional level

    Temperature sensing through DNA involves local DNA topological change followed by transcriptional event. For example, the thesis of transcription factor σ32 in E.Coli increases rapidly when temperature upshift, which could mediate the transcription of genes that have σ32 -recognizing promoters[5](figure 2). But this regulatory pathway takes some time to come into effect because the thermosensing proteins required time for upregulation[1].

    2.Translational level

    Temperature sensing also bases on many types of thermoregulatory RNA elements, also known for RNA-based thermosensors (RTSs), which are located in the 5’ untranslated region (5’ UTR) of mRNA[6]. The 5’ UTR is a part of bacterial transcript of gene, which would not be translated into peptide. Therefore, RTSs are none-coding RNA elements. These types of thermoregulation respond to temperature and modulate the translation of already existing or nascent mRNAs, which could induce altered mRNA stability and ribosome accessibility of ribosome binding site (RBS) thereby controlling the translation efficiency (figure 3).

    3.Post-translational level

    Unfolded or incorrect protein conformation is the most example of the consequences of temperature-induced damages. When temperature upshifts, chaperone proteins that are overexpressed can promote nascent polypeptide chains to fold into correct conformation, which is known as post-translational thermoregulation[7,8](figure 4). But this process is more like to lock the barn door after the horse was stolen, meaning cellular processes have already been altered due to temperature shifts.

  • References

    • [1]Kortmann J, Narberhaus F. Bacterial RNA thermometers: molecular zippers and switches.[J]. Nature Reviews Microbiology, 2012, 10(4):255-65.
    • [2]Abduljalil J M. Bacterial riboswitches and RNA thermometers: Nature and contributions to pathogenesis[J]. Non-coding RNA Research, 2018, 3(2):54-63.
    • [3]Angel E. Garcia,† and, Dietmar Paschek‡. Simulation of the Pressure and Temperature Folding/Unfolding Equilibrium of a Small RNA Hairpin[J]. Journal of the American Chemical Society, 2008, 130(3):815-7.
    • [4]Inaba M, Suzuki I, Szalontai B, et al. Gene-engineered Rigidification of Membrane Lipids Enhances the Cold Inducibility of Gene Expression in Synechocystis[J]. Journal of Biological Chemistry, 2003, 278(14):12191.
    • [5]Guisbert E, Yura T, Rhodius V A, et al. Convergence of molecular, modeling, and systems approaches for an understanding of the Escherichia coli heat shock response.[J]. Microbiology & Molecular Biology Reviews Mmbr, 2008, 72(3):545-54.
    • [6]Grosso-Becera M V, Servín-González L, Soberón-Chávez G. RNA structures are involved in the thermoregulation of bacterial virulence-associated traits[J]. Trends in Microbiology, 2015, 23(8):509-518.
    • [7]Tomoyasu T, Ogura T, Tatsuta T, et al. Levels of DnaK and DnaJ provide tight control of heat shock gene expression and protein repair in Escherichia coli[J]. Molecular Microbiology, 2010, 30(3):567-581.
    • [8]Langer T, Lu C, Echols H, et al. Successive action of DnaK, DnaJ and GroEL along the pathway of chaperone-mediated protein folding.[J]. Nature, 1992, 356(6371):683-689.