The synthesis of peptides can be done in different ways

These methods include peptide production using recombinant DNA technology, chemical synthesis, biosynthesis and using enzyme technology.

The size of the molecule determines the appropriate method for peptide production. Recombinant DNA technology is suitable for the synthesis of large peptides and proteins. Chemical synthesis is a suitable technology for the production of small and medium-sized peptides that have 5 to 80 amino acids. Enzymatic synthesis is more limited and is hardly used for the synthesis of peptides longer than 10 amino acids. In this sense, peptide production technologies are not competitive with each other in most cases.

1. Recombinant DNA technology

Due to the advances obtained from molecular cellular mechanisms, experts have succeeded in using recombinant DNA technology to produce new compounds with high efficiency. The use of recombinant DNA technology has resulted in the production of more than 400 therapeutic proteins and peptides, and so far more than 200 of them have been approved by the US Food and Drug Administration (FDA). Insulin, albumin, interferons, human growth hormones and monoclonal antibodies are the ones that have been considered therapeutically.

2. Chemical method

For the synthesis of medium-sized peptides, chemical methods are better than biotechnological methods such as recombinant DNA and biocatalysis, and often include molecules in the field of pharmaceuticals. It is also an essential tool for understanding the relationship between structure and function in proteins and peptides, discovering new therapeutic and diagnostic agents, and producing synthetic vaccines. The chemical synthesis of peptides is carried out in two ways: the synthesis of peptides in solution and the synthesis of peptides in solid phase, which has become more important since the introduction of solid phase synthesis by Merrifield.

1.2. Synthesis of peptides in solution phase (LPPS)

For small peptides that consist of only a few amino acids, the peptide synthesis method in the solution phase is suitable. In this method, the protected amino acid or primary parts react in the solution environment, and after that, the synthesized compound is purified to participate in the next stage reaction. The characteristic feature of this method is that it is possible to isolate and purify the intermediate after each synthesis step, and after deprotection, the conditions for the next amino acid connection are provided to obtain the desired peptide sequence.

For the synthesis of short peptide chains on a large scale, the synthesis of cyclic peptides and the synthesis using unusual amino acids, mostly the solution phase method or a combination of the synthesis method in the solution and solid phase is recommended. Despite the advantages mentioned for the synthesis method in the solution phase, this method is slower and has a lower efficiency than the synthesis in the solid phase.

2.2. Solid phase peptide synthesis (APPS)

Peptide synthesis in the solid phase is such that the end carbon of the amino acid is attached to a stationary phase and by sequentially adding amino acids through reactions that are repeated cyclically, the peptide chain is lengthened. When Merrifield introduced the solid-phase synthesis method in 1963, the scientific community reacted with skepticism because solution synthesis was well known by then.

Solid phase synthesis has many advantages over peptide synthesis in the solution phase: due to the presence of controlled steps in the peptide synthesis using the solid phase method, the reaction can be performed automatically, and there is no longer the problem of the peptide dissolving because it is connected to the solid phase. The type of protecting groups (Fmoc or t-Boc), the nature of the resin, the type of coupling and activating reagents, the separation of the peptide from the resin are the most important variables in SPPS.

3. Biosynthesis

Ribosomes can synthesize peptides using information contained in mRNA molecules and with the help of tRNA molecules and protein factors. One of the disadvantages of this method is the low scale of synthesis, and in addition, not all peptides can be produced by biosynthesis. In the synthesis by chemical methods, amino acids needed a protective group, but in the biosynthesis method, amino acids are without protective groups.

4. Use of enzyme technology

Enzymes are biological catalysts that are responsible for cellular metabolism. Cells need mild conditions to function properly, and enzymes work well in these conditions, but to become process biocatalysts, they must be strong enough to withstand the harsh conditions of an industrial process. Therefore, choosing the right enzyme in industrial processes is very important. Proteolytic enzymes form a group of hydrolases that are suitable for industrial conditions. Microbial and plant proteases have been widely used in medicine and in various industrial processes. Due to the fact that proteases are active and stable under mild pH conditions in the range of 6 to 8, and in addition, they are very space-selective and displacement-selective, proteases have been used as catalysts in the synthesis of organic compounds. In addition to catalyzing the formation of peptide bonds, proteases can also catalyze the breaking of peptide bonds. Compared to chemical synthesis, the most important advantage of the biocatalysis method is that it reduces the need for side chain protection. Enzymatically synthesized small peptides (usually di- or tripeptides) are used as drugs as well as agrochemicals. Some examples synthesized using enzyme technology include the calorie-free sweetener aspartame, kytorphin, angiotensin, enkephalin and dynorphin. Telios pharmaceutical company has investigated the enzymatic synthesis of Arg-Gly-Asp tripeptide as a new drug for healing heavy burns and skin wounds. Several other examples of enzymatically synthesized peptides have also been reported in the last decade.

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