Some of the oldest bacteria on the planet are classified as thermophiles – or, bacteria who thrive under high temperature conditions. In places like hot springs and oceanic hydrothermal vents, which can reach up to 122 degrees Fahrenheit, such bacteria still flourish today. While many other organisms – including cooler temperature-loving bacteria known as mesophiles – would die under such conditions, thermophiles prosper.

Why can certain organisms survive these conditions and others cannot? One of the major factors surrounding this phenomenon is the proteins involved within the cellular structure of each bacterium, and the temperatures at which they experience a form of breakdown known as denaturation. The process behind protein denaturation and its contribution to cell death are currently the subject of much research. 

What Is Protein Denaturation? 

The primary state of a protein is several chains of amino acids. To perform its function, a protein must undergo folding, which changes its shape and exposes different bonding sites on its surface. Folding multiple times into secondary, tertiary, and quaternary structures is what allows protein to carry out its duties within a cell. 

In general, denaturation is the process by which either a protein or a nucleic acid undergoes changes and loses its higher structures, leaving it in its primary state. Denaturation is brought on by some external stress, such as heat or radiation, or another compound like a strong acid or base, solvent, or a salt. Once the protein enters its primary state, it can often no longer perform the functions permitted by its functional state.

What Are the Effects of Protein Denaturation?

An egg white is one of the best examples of protein denaturation. When you introduce an egg white to a hot pan, the clear, slippery white is almost immediately transformed into opaque, firm egg white. This occurs when the egg’s albumins denature due to the heat, aggregate, and solidify.

Different proteins experience denaturation under different circumstances. However, once a protein reaches its unique temperature, radiation, or chemical threshold, the functional structures collapse. What that collapse does to the surrounding cell can differ between proteins, as can its reversibility. For example, the denatured protein in an enzyme is rendered useless because its binding sites are no longer prominent, a state which is often irreversible. 

How Does Denaturation and Protein Collapse Affect Cells?

Once a protein experiences denaturation and collapses to assume its primary structure, a number of different events may occur. Some proteins aggregate with others of their own kind, while others solidify. Still others do both; research has found that some of these proteins are associated with Alzheimer’s, Parkinson’s, and other neurodegenerative disorders. When enough proteins denature and collapse, a cell dies.

It was once assumed that when the cell reaches the temperature threshold, most proteins would collapse, leading to cell death. However, recent research shows that only a small number of key rare proteins need collapse before cell death occurs. This discovery is significant in thermophilic bacteria research. 

Studies performed comparing known thermophilic bacterium T. thermophilus, yeast, E. coli, and human cells showed that only a few proteins in each actually collapsed immediately before cell death. These rare proteins all had key cell functions; thus, their collapse and the resulting loss of function left the cell unable to sustain life. However, even the most crucial parallel proteins in the T. thermophilus bacteria remained stable, allowing the cell to live.

Moving Forward

Studies regarding the protein stability of T. thermophilus and other thermophilic bacteria may reveal more insight into similar proteins found in humans. Eventually, methods by which researchers could stabilize the human proteins currently susceptible to denaturation may be found, leading to prevention or therapies for Alzheimer’s, Parkinson’s, and other disorders caused by protein instability.