Thermostable

Thermostability is the quality of a substance to resist irreversible change in its chemical or physical structure, often by resisting decomposition or polymerization, 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 is also a property of some proteins. To be a thermostable protein means to be resistant to changes in protein structure due to applied heat.

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 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. 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. Other factors of protein thermostability are compactness of protein structure, oligomerization, and strength interaction between subunits.

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