Thermostability

Crystal structure of β-glucosidase from Thermotoga neapolitana (PDB: 5IDI). Thermostable protein, active at 80°C and with unfolding temperature of 101°C.[1]

Thermostability is the quality of a substance to resist irreversible change in its chemical or physical structure, often by resisting decomposition or polymerisation, at a high relative temperature.

Thermostable materials may be used industrially as fire retardants. A thermostable plastic, an uncommon and unconventional term, is likely to refer to a thermosetting plastic that cannot be reshaped when heated, than to a thermoplastic that can be remelted and recast. Thermostability also commonly refers to a protein resistant to change in its protein structure due to applied heat.

Thermostable proteins

Most life-forms on Earth live at temperatures of less than 50 °C, commonly from 15 to 50 °C. Above this, thermal energy may cause the unfolding of the protein structure, where the activity of the protein is abolished and a condition understandably deleterious to continuing life-functions. The denaturing of proteins in albumen from a clear, nearly colourless liquid to an opaque white, insoluble gel is a common example of this.

Certain thermophilic life-forms exist which can withstand temperatures above this, and have corresponding adaptations to preserve protein function at these temperatures.[2] These can include altered bulk properties of the cell to stabilize all proteins,[3] and specific changes to individual proteins. Examining homologous proteins present in these thermophiles and other organisms reveal only slight differences in the protein structure. One notable difference is the presence of extra hydrogen bonds in the thermophile's proteins—meaning that the protein structure is more resistant to unfolding. The presence of certain types of salt has been observed to alter thermostability in the proteins, indicating that salt bridges likely also play a role in thermostability.[4] Other factors of protein thermostability are compactness of protein structure,[5] oligomerization,[6] and strength interaction between subunits.

Thermostable enzymes such as Taq polymerase and Pfu DNA polymerase are used in polymerase chain reactions where temperatures of 94 °C or over are used to melt apart DNA strands.[7]

Another important group of thermostable enzymes are glycoside hydrolases. These enzymes are responsible of the degradation of the major fraction of biomass, the polysaccharides present in starch and lignocellulose. Thus, glycoside hydrolases are gaining great interest in biorefining applications in the future bioeconomy.[8] Some examples are the production of monosaccharides for food applications as well as use as carbon source for microbial conversion in fuels (ethanol) and chemical intermediates, production of oligosaccharides for prebiotic applications and production of surfactants alkyl glycoside type. All of these processes often involve thermal treatments to facilitate the polysaccharide hydrolysis, hence give thermostable variants of glycoside hydrolases an important role in this context.

Approaches to improve thermostability of proteins

Protein engineering can be used to enhance the thermostability of proteins. A number of site-directed and random mutagenesis techniques,[9][10] in addition to directed evolution,[11] have been used to increase the thermostability of target proteins. Comparative methods have been used to increase the stability of mesophilic proteins based on comparison to thermophilic homologs.[12][13][14][15] Additionally, analysis of the protein unfolding by molecular dynamics can be used to understand the process of unfolding and then design stabilizing mutations.[16] Rational protein engineering for increasing protein thermostability includes mutations which truncate loops, increase salt bridges[17] or hydrogen bonds, introduced disulfide bonds.[18] In addition, ligand binding can increase the stability of the protein, particularly when purified.[19]

Thermostable toxins

Certain poisonous fungi contain thermostable toxins, such as amatoxin found in the death cap and autumn skullcap mushrooms and patulin from molds. Therefore, applying heat to these will not remove the toxicity and is of particular concern for food safety.[20]

See also

Thermophiles

References

  1. ↑ Kulkarni, T.S.; Khan, S.; Villagomez, R.; Mahmood, T.; Lindahl, S.; Logan, D.T.; Linares‐Pastén, J.A.; Nordberg Karlsson, E. (2017). "Crystal structure of β‐glucosidase 1A from Thermotoga neapolitana and comparison of active site mutants for hydrolysis of flavonoid glucosides". Proteins: Structure, Function, and Bioinformatics. 85 (5): 872–884. doi:10.1002/prot.25256.
  2. ↑ Takami, H; Takaki, Y; Chee, G. J.; Nishi, S; Shimamura, S; Suzuki, H; Matsui, S; Uchiyama, I (2004). "Thermoadaptation trait revealed by the genome sequence of thermophilic Geobacillus kaustophilus". Nucleic Acids Research. 32 (21): 6292–303. PMC 535678 Freely accessible. PMID 15576355. doi:10.1093/nar/gkh970.
  3. ↑ Neves, C; Da Costa, M. S.; Santos, H (2005). "Compatible solutes of the hyperthermophile Palaeococcus ferrophilus: Osmoadaptation and thermoadaptation in the order thermococcales". Applied and Environmental Microbiology. 71 (12): 8091–8. PMC 1317470 Freely accessible. PMID 16332790. doi:10.1128/AEM.71.12.8091-8098.2005.
  4. ↑ Das, R; Gerstein, M (2000). "The stability of thermophilic proteins: A study based on comprehensive genome comparison". Functional & Integrative Genomics. 1 (1): 76–88. PMID 11793224. doi:10.1007/s101420000003.
  5. ↑ Thompson, M. J.; Eisenberg, D (1999). "Transproteomic evidence of a loop-deletion mechanism for enhancing protein thermostability". Journal of Molecular Biology. 290 (2): 595–604. PMID 10390356. doi:10.1006/jmbi.1999.2889.
  6. ↑ Tanaka, Y; Tsumoto, K; Yasutake, Y; Umetsu, M; Yao, M; Fukada, H; Tanaka, I; Kumagai, I (2004). "How oligomerization contributes to the thermostability of an archaeon protein. Protein L-isoaspartyl-O-methyltransferase from Sulfolobus tokodaii". Journal of Biological Chemistry. 279 (31): 32957–67. PMID 15169774. doi:10.1074/jbc.M404405200.
  7. ↑ Saiki, R. K.; Gelfand, D. H.; Stoffel, S; Scharf, S. J.; Higuchi, R; Horn, G. T.; Mullis, K. B.; Erlich, H. A. (1988). "Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase". Science. 239 (4839): 487–91. PMID 2448875. doi:10.1126/science.2448875.
  8. ↑ Linares-Pastén, J. A.; Andersson, M; Nordberg karlsson, E (2014). "Thermostable glycoside hydrolases in biorefinery technologies". Current Biotechnology. 3 (1): 26–44. doi:10.2174/22115501113026660041.
  9. ↑ Sarkar, C. A.; Dodevski, I; Kenig, M; Dudli, S; Mohr, A; Hermans, E; Plückthun, A (2008). "Directed evolution of a G protein-coupled receptor for expression, stability, and binding selectivity". Proceedings of the National Academy of Sciences. 105 (39): 14808–13. Bibcode:2008PNAS..10514808S. PMC 2567449 Freely accessible. PMID 18812512. doi:10.1073/pnas.0803103105.
  10. ↑ Asial, I; Cheng, Y. X.; Engman, H; Dollhopf, M; Wu, B; Nordlund, P; Cornvik, T (2013). "Engineering protein thermostability using a generic activity-independent biophysical screen inside the cell". Nature Communications. 4: 2901. Bibcode:2013NatCo...4E2901A. PMID 24352381. doi:10.1038/ncomms3901.
  11. ↑ Hoseki, J; Yano, T; Koyama, Y; Kuramitsu, S; Kagamiyama, H (1999). "Directed evolution of thermostable kanamycin-resistance gene: A convenient selection marker for Thermus thermophilus". Journal of Biochemistry. 126 (5): 951–6. PMID 10544290. doi:10.1093/oxfordjournals.jbchem.a022539.
  12. ↑ Sayed, A; Ghazy, M. A.; Ferreira, A. J.; Setubal, J. C.; Chambergo, F. S.; Ouf, A; Adel, M; Dawe, A. S.; Archer, J. A.; Bajic, V. B.; Siam, R; El-Dorry, H (2014). "A novel mercuric reductase from the unique deep brine environment of Atlantis II in the Red Sea". Journal of Biological Chemistry. 289 (3): 1675–87. PMC 3894346 Freely accessible. PMID 24280218. doi:10.1074/jbc.M113.493429.
  13. ↑ Perl, D; Mueller, U; Heinemann, U; Schmid, F. X. (2000). "Two exposed amino acid residues confer thermostability on a cold shock protein". Nature Structural Biology. 7 (5): 380–3. PMID 10802734. doi:10.1038/75151.
  14. ↑ Lehmann, M; Pasamontes, L; Lassen, S. F.; Wyss, M (2000). "The consensus concept for thermostability engineering of proteins". Biochimica et Biophysica Acta. 1543 (2): 408–415. PMID 11150616. doi:10.1016/s0167-4838(00)00238-7.
  15. ↑ Sauer, DB; Karpowich, NK; Song, JM; Wang, DN (6 October 2015). "Rapid Bioinformatic Identification of Thermostabilizing Mutations.". Biophysical Journal. 109 (7): 1420–8. PMC 4601007 Freely accessible. PMID 26445442. doi:10.1016/j.bpj.2015.07.026.
  16. ↑ Liu, H. L.; Wang, W. C. (2003). "Protein engineering to improve the thermostability of glucoamylase from Aspergillus awamori based on molecular dynamics simulations". Protein engineering. 16 (1): 19–25. PMID 12646689. doi:10.1093/proeng/gzg007.
  17. ↑ Lee, C. W.; Wang, H. J.; Hwang, J. K.; Tseng, C. P. (2014). "Protein thermal stability enhancement by designing salt bridges: A combined computational and experimental study". PLOS ONE. 9 (11): e112751. PMC 4231051 Freely accessible. PMID 25393107. doi:10.1371/journal.pone.0112751.
  18. ↑ Mansfeld, J; Vriend, G; Dijkstra, B. W.; Veltman, O. R.; Van Den Burg, B; Venema, G; Ulbrich-Hofmann, R; Eijsink, V. G. (1997). "Extreme stabilization of a thermolysin-like protease by an engineered disulfide bond". The Journal of Biological Chemistry. 272 (17): 11152–6. PMID 9111013. doi:10.1074/jbc.272.17.11152.
  19. ↑ Mancusso, R; Karpowich, N. K.; Czyzewski, B. K.; Wang, D. N. (2011). "Simple screening method for improving membrane protein thermostability". Methods. 55 (4): 324–9. PMC 3220791 Freely accessible. PMID 21840396. doi:10.1016/j.ymeth.2011.07.008.
  20. ↑ "FDA: Moldy applesauce repackaged by school lunch supplier". NBC News. NBC News. Retrieved 15 April 2015.
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