Denaturation and Protein Folding (OpenStax Biology 2e)
Each protein has its own unique sequence and shape that chemical interactions hold together. If the protein is subject to changes in temperature, pH, or exposure to chemicals, the protein structure may change, losing its shape without losing its primary sequence in what scientists call denaturation. Denaturation is often reversible because the polypeptide’s primary structure is conserved in the process if the denaturing agent is removed, allowing the protein to resume its function. Sometimes denaturation is irreversible, leading to loss of function. One example of irreversible protein denaturation is frying an egg. The albumin protein in the liquid egg white denatures when placed in a hot pan. Not all proteins denature at high temperatures. For instance, bacteria that survive in hot springs have proteins that function at temperatures close to boiling. The stomach is also very acidic, has a low pH, and denatures proteins as part of the digestion process; however, the stomach’s digestive enzymes retain their activity under these conditions.
Protein folding is critical to its function. Scientists originally thought that the proteins themselves were responsible for the folding process. Only recently researchers discovered that often they receive assistance in the folding process from protein helpers, or chaperones (or chaperonins) that associate with the target protein during the folding process. They act by preventing polypeptide aggregation that comprise the complete protein structure, and they disassociate from the protein once the target protein is folded.– What is the state in which proteins are properly folded and/or assembled that makes it operative and functional?
A classic example of denaturing in proteins comes from egg whites, which are typically largely egg albumins in water. Fresh from the eggs, egg whites are transparent and liquid. Cooking the thermally unstable whites turns them opaque, forming an interconnected solid mass. The same transformation can be effected with a denaturing chemical. Pouring egg whites into a beaker of acetone will also turn egg whites translucent and solid.
Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e
Date Published: April 9, 2012 Publisher: Public Library of Science Author(s): Enrique Hernández-Lemus, Luz Adriana Nicasio-Collazo, Ramón Castañeda-Priego, Alejandro Raul Hernandez Montoya. http://doi.org/10.1371/journal.pone.0033789 Abstract: In the past, a great deal of attention has been drawn to thermal driven denaturation processes. In recent years, however, the discovery of stress-induced denaturation, observed at the one-molecule level, has revealed … Continue reading
Date Published: April 20, 2017 Publisher: Public Library of Science Author(s): Aldona Jelińska, Anna Zagożdżon, Marcin Górecki, Agnieszka Wisniewska, Jadwiga Frelek, Robert Holyst, Eugene A. Permyakov. http://doi.org/10.1371/journal.pone.0175838 Abstract: We showed that the Taylor Dispersion Analysis (TDA) is a fast and easy to use method for the study of denaturation proteins. We applied TDA to study … Continue reading
Date Published: April 21, 2016 Publisher: Public Library of Science Author(s): Vera A. Borzova, Kira A. Markossian, Natalia A. Chebotareva, Sergey Yu. Kleymenov, Nikolay B. Poliansky, Konstantin O. Muranov, Vita A. Stein-Margolina, Vladimir V. Shubin, Denis I. Markov, Boris I. Kurganov, Eugene A. Permyakov. http://doi.org/10.1371/journal.pone.0153495 Abstract: Thermal aggregation of bovine serum albumin (BSA) has been … Continue reading
Date Published: July 21, 2015 Publisher: Public Library of Science Author(s): Andrea Pica, Giuseppe Graziano, Piero Andrea Temussi. http://doi.org/10.1371/journal.pone.0133550 Abstract: Both sodium chloride and sodium sulfate are able to stabilize yeast frataxin, causing an overall increase of its thermodynamic stability curve, with a decrease in the cold denaturation temperature and an increase in the hot … Continue reading
Date Published: November 14, 2008 Publisher: Public Library of Science Author(s): Martin C. Stumpe, Helmut Grubmüller, Vijay S. Pande Abstract: Urea-induced protein denaturation is widely used to study protein folding and stability; however, the molecular mechanism and driving forces of this process are not yet fully understood. In particular, it is unclear whether either hydrophobic … Continue reading