In
materials science
Materials science is an interdisciplinary field of researching and discovering materials. Materials engineering is an engineering field of finding uses for materials in other fields and industries.
The intellectual origins of materials sci ...
and
molecular biology
Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...
, thermostability is the ability of a
substance to resist irreversible change in its
chemical
A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...
or physical structure, often by resisting
decomposition
Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ess ...
or
polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
, at a high relative
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
.
Thermostable materials may be used industrially as
fire retardant
A fire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce the flammability of fuels or delay their combustion. Fire retardants ...
s. A ''thermostable
plastic
Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
'', an uncommon and unconventional term, is likely to refer to a
thermosetting plastic that cannot be reshaped when heated, than to a
thermoplastic
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains as ...
that can be remelted and recast.
Thermostability is also a property of some
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s. To be a thermostable protein means to be resistant to changes in
protein structure
Protein structure is the three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, which are the monomers of the polymer. A single amino acid ...
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. Within these organisms are macromolecules (proteins and nucleic acids) which form the three-dimensional structures essential to their enzymatic activity. Above the native temperature of the organism, thermal energy may cause the
unfolding and
denaturation, as the heat can disrupt the intramolecular bonds in the tertiary and quaternary structure. This unfolding will result in loss in enzymatic activity, which is understandably deleterious to continuing life-functions. An example of such is the denaturing of proteins in
albumen
Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens, it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms aro ...
from a clear, nearly colourless liquid to an opaque white, insoluble gel.
Proteins capable of withstanding such high temperatures compared to proteins that cannot, are generally from microorganisms that are hyperthermophiles. Such organisms can withstand above 50 °C temperatures as they usually live within environments of 85 °C and above.
Certain
thermophilic life-forms exist which can withstand temperatures above this, and have corresponding adaptations to preserve protein function at these temperatures. These can include altered bulk properties of the cell to stabilize all proteins, and specific changes to individual proteins. Comparing
homologous proteins present in these thermophiles and other organisms reveal some differences in the protein structure. One notable difference is the presence of extra
hydrogen bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...
s in the thermophile's proteins—meaning that the protein structure is more resistant to unfolding. Similarly, thermostable proteins are rich in
salt bridges or/and extra
disulfide bridges stabilizing the structure. Other factors of protein thermostability are compactness of protein structure, oligomerization, and strength interaction between subunits.
Uses and applications
Polymerase chain reactions
Thermostable DNA polymerase
Thermostable DNA polymerases are DNA polymerases that originate from thermophiles, usually bacterial or archaeal species, and are therefore thermostable. They are used for the polymerase chain reaction and related methods for the amplification a ...
s such as
Taq polymerase
''Taq'' polymerase is a thermostable DNA polymerase I named after the thermophilic eubacterial microorganism ''Thermus aquaticus,'' from which it was originally isolated by master's student Alice Chien et al. in 1976. Its name is often abbr ...
and
Pfu DNA polymerase are used in
polymerase chain reaction
The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...
s (PCR) where temperatures of 94 °C or over are used to melt
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
strands in the denaturation step of PCR. This resistance to high temperature allows for DNA polymerase to elongate DNA with a desired sequence of interest with the presence of dNTPs.
Feed additives
Enzymes are often added to animal feed to improve the health and growth of farmed animals, particularly chickens and pigs. The feed is typically treated with high pressure steam to kill bacteria such as
Salmonella
''Salmonella'' is a genus of bacillus (shape), rod-shaped, (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two known species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' ...
. Therefore the added enzymes (e.g.
phytase
A phytase (''myo''-inositol hexakisphosphate phosphohydrolase) is any type of phosphatase enzyme that catalyzes the hydrolysis of phytic acid (myo-inositol hexakisphosphate) – an indigestible, organic form of phosphorus that is found in many pla ...
and
xylanase) must be able to withstand this thermal challenge without being irreversibly inactivated.
Protein purification
Knowledge of an enzyme's resistance to high temperatures is especially beneficial in
protein purification
Protein purification is a series of processes intended to isolate one or a few proteins from a complex mixture, usually Cell biology, cells, Tissue (biology), tissues, or whole organisms. Protein purification is vital for the specification of the ...
. In the procedure of heat denaturation, one can subject a mixture of proteins to high temperatures, which will result in the denaturation of proteins that are not thermostable, and the isolation of the protein that is thermodynamically stable. One notable example of this is found in the purification of
alkaline phosphatase from the hyperthermophile ''
Pyrococcus abyssi''. This enzyme is known for being heat stable at temperatures greater than 95 °C, and therefore can be partially purified by heating when heterologously expressed in ''E. coli''. The increase in temperature causes the ''E. coli'' proteins to precipitate, while the ''P. abyssi'' alkaline phosphatase remains stably in solution.
Glycoside hydrolases
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. 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, in addition to
directed evolution, have been used to increase the thermostability of target proteins. Comparative methods have been used to increase the stability of
mesophilic
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37 °C (about 99 °F). The term is mainly applied ...
proteins based on comparison to
thermophilic
A thermophile is a type of extremophile that thrives at relatively high temperatures, between . Many thermophiles are archaea, though some of them are bacteria and fungi. Thermophilic eubacteria are suggested to have been among the earliest bact ...
homologs. Additionally, analysis of the protein unfolding by
molecular dynamics
Molecular dynamics (MD) is a computer simulation method for analyzing the Motion (physics), physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamics ( ...
can be used to understand the process of unfolding and then design stabilizing mutations. Rational protein engineering for increasing protein thermostability includes mutations which truncate loops, increase salt bridges or hydrogen bonds, introduced
disulfide bonds. In addition, ligand binding can increase the stability of the protein, particularly when purified. There are various different forces that allow for the thermostability of a particular protein. These forces include hydrophobic interactions, electrostatic interactions, and the presence of disulfide bonds. The overall amount of hydrophobicity present in a particular protein is responsible for its thermostability. Another type of force that is responsible for thermostability of a protein is the electrostatic interactions between molecules. These interactions include salt bridges and hydrogen bonds. Salt bridges are unaffected by high temperatures, therefore, are necessary for protein and enzyme stability. A third force used to increase thermostability in proteins and enzymes is the presence of disulfide bonds. They present covalent cross-linkages between the polypeptide chains. These bonds are the strongest because they're covalent bonds, making them stronger than intermolecular forces.
Glycosylation
Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...
is another way to improve the thermostability of proteins.
Stereoelectronic effects in stabilizing interactions between carbohydrate and protein can lead to the thermostabilization of the glycosylated protein.
Cyclizing enzymes by covalently linking the N-terminus to the C-terminus has been applied to increase the thermostability of many enzymes.
Intein cyclization and
SpyTag/SpyCatcher cyclization have often been employed.
Thermostable toxins
Certain
poison
A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...
ous
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
contain thermostable
toxin
A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...
s, such as
amatoxin
Amatoxins are a subgroup of at least nine related cyclic peptide toxins found in three genera of deadly poisonous mushrooms (''Amanita'', '' Galerina'' and '' Lepiota'') and one species of the genus '' Pholiotina''. Amatoxins are very potent, as li ...
found in the
death cap
''Amanita phalloides'' ( ), commonly known as the death cap, is a deadly poisonous basidiomycete fungus and mushroom, one of many in the genus ''Amanita''. Originating in Europe but later introduced to other parts of the world since the late ...
and
autumn skullcap mushroom
A mushroom or toadstool is the fleshy, spore-bearing Sporocarp (fungi), fruiting body of a fungus, typically produced above ground on soil or another food source. ''Toadstool'' generally refers to a poisonous mushroom.
The standard for the n ...
s and
patulin from molds. Therefore, applying heat to these will not remove the toxicity and is of particular concern for food safety.
See also
;Thermophiles
* ''
Thermus thermophilus''
* ''
Thermus aquaticus
''Thermus aquaticus'' is a species of bacteria that can tolerate high temperatures, one of several thermophile, thermophilic bacteria that belong to the ''Deinococcota'' phylum. It is the source of the heat-resistant enzyme Taq polymerase, ''Taq' ...
''
* ''
Pyrococcus furiosus''
References
External links
Thermostability of Proteins{{Webarchive, url=https://web.archive.org/web/20160622080649/http://homepages.uel.ac.uk/S.Doonan/thermo.html , date=2016-06-22
Protein structure
Toxicology
Extremophiles