What is Protein Denaturation?
When a protein faces environmental stresses, what usually happens to it?
When RNA is translated into individual amino acids, it eventually forms a long chain of amino acids. The chain is called protein on its primary structure. When the protein reaches its tertiary or quaternary conformation, it is said to be on functional state and can perform its function. The quaternary structure is held in place by both intermolecular (between polypeptide chains) and intramolecular bonds and also stabilized by many weak interactions. Its arrangement is in such a way that the hydrophobic regions are hidden from the aqueous environment.
For proteins, their conformation or arrangement is everything. Naturally, the arrangement of amino acids determines its shape but it is the shape that eventually determines the protein function. Here lies the problem. When our bodies get exposed to environmental stresses and yes, we frequently get exposed to them, we may not feel the effects immediately. The adverse effects occur in molecular level—in the bonds that hold these proteins in shape.
Common environmental stresses include heat (e.g. from overexposure to tanning beds and sunlight), suboptimal pH, heavy metal salts, so on.
What happens to the proteins when exposed to these stresses?
- In quaternary structure, the intramolecular and intermolecular bonds get disrupted. The many weak interactions that stabilize the protein would also be affected.
- In tertiary structure, the weak interactions such as hydrogen bonds and Van der Waals forces get affected as well as the ionic and disulphide bonds. If those are not enough, the hydrophobic forces that are usually hidden from the aqueous environment become exposed.
- In secondary structure, the intermolecular (beta sheet) and intramolecular (alpha-helix) forces that cause the protein to fold initially, become disrupted. (Note: The shape of a protein molecule is caused by the hydrogen-bonding between –C=O and -N-H groups within the chain).
- In primary structure, if the stress reaches this irreversible point, it would affect the arrangement of the amino acids. When the amino acid sequences get altered, it would affect not only the final conformation of the protein but also its function.
One classic example to further explain this protein denaturation is the egg. A normal egg has native and functional proteins inside the shell. When it is broken and heated up (note that heat is a stress source), the heat energy is enough to break the weak forces that hold the quaternary protein into place. This causes the protein to unfold to its tertiary or secondary conformation. This unfolding causes the hydrophobic regions to become exposed to the aqueous environment. Since the peptide bonds that hold the amino acids together are highly hydrophilic, they would attract water molecules. Hydrophobic regions that are exposed to the water become highly unstable and tend to form new associations of Hydrophobic-Hydrophobic forces. This arrangement is random and considered very strong.
Lo and behold, we finally get the coagulated white of our sunny side up.