Difference between revisions of "Team:Jilin China/Background"
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<p>There are always challenges for bacterial survival, especially to keep suitable living status facing fluctuations of chemical and physical parameters<sup>[1]</sup>. 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, since the efficiency of all cellular processes is temperature dependent, especially the expression of any given gene<sup>[2,3]</sup>. Therefore, it is indispensable for bacteria to evolve more sensitive and more effective abilities, which can respond to temperature forwardly before the damages such as unfolded proteins or membrane rigidification occur<sup>[4]</sup> (figure 1).</p> | <p>There are always challenges for bacterial survival, especially to keep suitable living status facing fluctuations of chemical and physical parameters<sup>[1]</sup>. 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, since the efficiency of all cellular processes is temperature dependent, especially the expression of any given gene<sup>[2,3]</sup>. Therefore, it is indispensable for bacteria to evolve more sensitive and more effective abilities, which can respond to temperature forwardly before the damages such as unfolded proteins or membrane rigidification occur<sup>[4]</sup> (figure 1).</p> | ||
<center><img src="https://static.igem.org/mediawiki/2018/a/a7/T--Jilin_China--Background--Physical_Chemical_Factor.svg" width="70%" /></center> | <center><img src="https://static.igem.org/mediawiki/2018/a/a7/T--Jilin_China--Background--Physical_Chemical_Factor.svg" width="70%" /></center> | ||
| + | <p class="figure">Figure 1. To survival in the change of many physical and chemical parameters, bacteria have evolved many kinds of biosensors to respond to its surroundings.</p> | ||
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Revision as of 14:08, 17 October 2018
Overview
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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, since the efficiency of all cellular processes is temperature dependent, especially the expression of any given gene[2,3]. Therefore, it is indispensable for bacteria to evolve more sensitive and more effective abilities, which can respond to temperature forwardly before the damages such as unfolded proteins or membrane rigidification occur[4] (figure 1).
Figure 1. To survival in the change of many physical and chemical parameters, bacteria have evolved many kinds of biosensors to respond to its surroundings.
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Biological signal transduction systems that sense temperature shifts
When it comes to the biological behavior of temperature sensing, it is crucial 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 in this level involves local DNA topological change followed by transcriptional event. For example, the expression of transcription factor σ32 in bacteria E.coli increases rapidly when temperature upshifts, which could mediate the transcription of genes including 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].
Figure 2. The example of transcriptonal thermoregulation (1) Heat-induced up-regulation of transcription factor σ32. (2) σ32 recognizes the specific promoters and recruits the core enzyme of RNA polymerase. (3) RNA ploymerase consisting of core enzyme and σ32 promote the transcriptional initiaion and elongation. (4) The heat-induced chaperones or peroteases are expressed increasingly.
2.Translational level
Temperature sensing also bases on many types of thermoregulatory RNA elements, also known for RNA-based thermosensors (RTs), 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, RTs 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).
>See more deatils about RTs，which are we focus on this year.<
Figure 3. The example of translational thermoregulation (A) At low temperatures, the stem-loop in 5’- UTR of mRNA hides the SD sequence by base-paring with vicinal anti-SD sequence. Ribosome could not bind to RBS and the translation switches OFF. (B) At high temperatures, the sem-loop melts, resulting the full liberation of the SD sequence and start coden. This conformational change promotes the entire ribosome accessibility of RBS. The translation switches ON.
3.Post-translational level
Unfolded or misfoled protein conformations are the most common 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, which means cellular processes have already been altered due to temperature shifts.
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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.