Proteolysis is the breakdown of proteins into their main components, peptides and amino acids, by hydrolysis of the peptide bonds that keep them together. Proteolysis may be used to regulate physiological activities by lowering protein concentrations, converting proteins into active forms, or giving amino acids needed to synthesise a new protein.
Proteases, enzymes that catalyse the breakdown of proteins, are often used in proteolysis. It may also happen as a consequence of unfavourable cellular circumstances such as high temperatures, acidity, or salinity, which disturb the molecules in the peptide bonds and cause the bonds to break.
The hydrolysis of the amide bond breaks down a peptide bond into its component amino acids.
When the peptide links that keep a protein together are hydrolyzed, this is known as proteolysis. Proteases, enzymes involved in the degradation of proteins, are often used to catalyse this. Based on the shape of the proteins and the amino acid residue to which they bind, the enzymes interact with them with substrate specificity. Exopeptidases and endopeptidases both break the amide bond between two amino acids at the amino or carboxy terminal, whereas endopeptidases cleave the protein inside the substrate (endopeptidases).
Aspartate, cysteine, glutamate, metallo, serine, and threonine proteases are the six categories of proteases classified by the manner in which they hydrolyze proteins and the residues involved. The amide bond is hydrolyzed either via an addition/elimination process that yields an intermediate or by direct hydrolysis of the bond by a polarised water molecule in the various categories.
Proteases, and hence proteolysis, may be stopped by binding inhibitors to the active sites of the protease or by spatial restriction of the protease from its substrates. This inhibition is crucial for the control of cellular activity.
Proteolysis serves a variety of critical but disparate functions in the body. It may either produce or remove proteins to influence protein function. Proteolysis may control a protein’s concentration by eliminating any excess protein, reducing or impairing its activity. Proteins are often completely inactivated by proteolysis, which may affect protein-protein interactions and signalling pathways, including apoptosis.
Proteases may also make active proteins by making small changes to a non-functioning or proto-protein, such as changing its physical state or position. Regulation of blood clotting by plasmin and fibrinolysis clearance of clots, and activation of the protease trypsin via alteration of the pre-protease zymogen are two examples.
By eliminating damaged or unneeded proteins, proteolysis also serves as a cellular cleaning mechanism. Proteins that have been shattered by another means, leaving just a protein fragment or misfolded proteins that are functionally impaired, are examples of damaged proteins. The amino acids will be recycled by the proteases to produce new or more suitable proteins, or they will be relocated to a different area. Proteins that are intact and folded appropriately are not broken down, basically functioning as a quality control function in the cell.
Proteolysis is an important part of food digestion since it breaks down any protein consumed so that the nutrients may be absorbed by the body. Proteins are entirely broken down into their amino acids during this process. Proteolysis is also used in the food industry. Proteases break down milk proteins in cheese manufacturing, and a low pH drives actin proteolysis in dry sausage fermentation.
Question and Answer
1.How does proteolysis break down a protein?
A is correct. Proteolysis breaks down the peptide bonds in a protein through hydrolysis of the amide bond. Hydrolysis is a chemical breakdown by reaction with water. The water molecule interacts with the amino on one amino acid, and the carboxy on the other.
2. What is an important function of proteolysis?
- formation of blood cells
- removal of toxins
- regulation of proteins
D is correct. Proteolysis can act to regulate proteins, signalling cascades, and gene expression, through the activation and repression of proteins through modification and breakdown of proteins.
3. What causes proteolysis?
- high temperatures
- extreme acidity
- all of the above
D is correct. While the majority of proteolysis is regulated by proteases (enzymes), it can also occur due to extreme environmental conditions which can disrupt chemical bonds.
Kaiser, M., Huber, R., & Ehrmann, M. (2013). “Proteolysis”. Brenner’s Encyclopedia of Genetics, 2nd ed. 501-503.