Biosynthesis and Regulation of Peptides

Amino acids are the building blocks of proteins and are the smallest unit in protein formation. Peptides are the polymers of amino acids. There are many peptides in the body and each has a different role in the body. Some of the benefits of peptides include anti-aging properties, acting as skin barrier, weight loss properties, etc.

Amino acids

Amino acid is made up of a combination of an amino group and a carboxyl group. It is amphoteric in nature as it has a basic and an acidic group. It means it can act as both acid and base. Amino acids are combined to form a long polypeptide chain of protein. 

There are mainly 20 amino acids based on their nature. These are:

• Alanine

• Arginine

• Asparagine

• Aspartic acid

• Cysteine

• Glutamine

• Glutamic acid

• Glycine

• Histidine

• Isoleucine

• Leucine

• Lysine

• Methionine

• Phenylalanine

• Proline

• Serine

• Threonine

• Tryptophan

• Tyrosine

• Valine

There are two categories of amino acids, namely

• Essential amino acid: It is the amino acid that is not naturally formed in the body and is obtained through a diet.

• Non-essential amino acid: These are the amino acids that are produced in the body and are not generally needed to be obtained through a diet.

Biosynthesis of peptides

Peptide structure is coded directly in the genome. It is easier for cells to produce peptides than a simple neurotransmitter. Peptide synthesis involves a protein precursor. In this precursor, the peptide sequence is embedded with specific proteolytic enzymes. This precursor protein is then packed in the vesicles. The active peptide is formed that is ready for release.

Production of peptides in which multiple amino acids are linked to form a long chain is known as peptide synthesis. Peptides are synthesised by the condensation reaction of the carboxyl group of one amino acid and amino group of the other.

Cellular level of peptide synthesis and release involves peptide formation by coupling of the carboxyl group of one amino acid to the amino group of another. Protecting groups is usually necessary  due to the possibility of unintended reactions. Chemical peptide synthesis usually starts at the C-terminal end of the peptide and ends at the N-terminus. 

It includes:

• Solid-phase synthesis

Each amino acid is attached to the chain of peptide N-terminus. Solid phase synthesis process has recurring cycles of alternate N-terminus deprotection and coupling reaction.

• Peptide coupling reagent

It is a crucial feature to enable the application of solid-phase synthesis. 

• Solid support

It is picked for physical stability and to allow rapid liquid filtration. 

• Protecting group schemes

It is important to protect the side chain groups at the time of synthesis of peptides to avoid unwanted side reactions. Unprotected side chain groups can lead to self-attaching of activated amino acids, leading to polymerisation. 

• Synthesising long peptides

It is ideal to use step-by-step connection of amino acids during elongation for small peptides having 2-100 residues of amino acids. One more method in the list is the fragment coupling method called fragment condensation.

Cellular mechanism for peptide synthesis and release

The proteins synthesised by ribosomes are polymerised by the membrane of the rough endoplasmic reticulum. Here, they are transported to golgi apparatus. In golgi apparatus, these are packed and stored in secretory vesicles. Further processing occurs within these transport and secretory vesicles. After this, the products formed are released through the process of exocytosis. Little material is stored in the secretory vesicles by constitutive secretion. Regulated secretion is done as a result of increased intracellular calcium ion level and then the material is stored in some amounts in secretory vesicles.

Regulation of peptides

Regulatory peptides are an important complex for information transfer between cells in different organs and tissues in the body. These are produced by all organisms.

Constitutive secretion 

It is a default pathway mainly used to renew material at plasma membranes and some membrane bound organelles. It is one of the pathways used by protein to be secreted and transferred out of the cell. In this pathway cells continuously secrete proteins regardless of the external signals.

Regulated secretion

It ends in the secretory vessels that are used to store secreted material till a signal starts fusion with the plasma membrane. In this type of secretion, the cell secretes proteins in large amounts when a specific signal is detected by the cell. It is generally used for proteins which are secreted when needed.

Conclusion

Thus, it can be concluded that there is no need for a special uptake mechanism for peptide synthesis and also for recapturing released mediators. Regulatory peptides are an important complex that helps to transfer the information to and fro the cell membrane.