What is polypeptide
Peptide is a compound formed by α – amino acid linked by peptide bond, which is the intermediate metabolite of protein. Generally speaking, polypeptides refer to
Peptide is a compound formed by α – amino acid linked by peptide bond, which is the intermediate metabolite of protein. Generally speaking, polypeptide refers to a compound formed by dehydration and condensation of less than 100 amino acids, with a relative molecular weight of less than 10000. Peptides have high bioactivity. At present, tens of thousands of endogenous peptides have been found, including hormones, growth factors, neuropeptides and other regulatory factors, which play an important role in the immune, nervous system, endocrine and so on.
Schematic diagram of peptide bond formation.
There are many methods of peptide synthesis, mainly including chemical synthesis and biosynthesis.
Chemical synthesis
Chemical synthesis is mainly realized by dehydration and condensation of amino acids. In the reaction process, the amino acids which do not need to be reflected in the raw materials are temporarily protected to ensure the directional synthesis. Chemical synthesis can be divided into solid phase synthesis and liquid phase synthesis, the main difference is whether to use solid phase carrier.
Liquid phase synthesis: there are two strategies for liquid phase synthesis, step-by-step synthesis and fragment combination. The step-by-step synthesis is simple and rapid, which is suitable for the synthesis of most polypeptides. The combination of fragments is conducive to the synthesis of larger polypeptides (containing more than 100 amino acids).
Solid phase synthesis: solid phase synthesis was founded by Merrifield in 1963. The principle is to fix the C-terminal of amino acids on insoluble resin, and then carry out condensation reaction in turn to extend peptide chain. The solid state synthesis method can be divided into Fmoc (9-fluorene methyl oxycarboxyl) and BOC (TERT butoxycarboxyl) methods.
BOC method takes BOC as the protective group of amino acid α – amino group, and benzyl alcohol as side chain protection group, which is a classical method, while Fmoc takes Fmoc as the protective group of amino acid α – amino group. Compared with BOC method, Fmoc method has the advantages of mild reaction conditions, high yield and less side reactions.
On the basis of the two traditional methods, scientists have gradually invented carboxylic acid glycoside method (NCA), combinatorial chemistry method, liquid phase step synthesis method and so on.
NCA method: the carboxylic anhydride of amino acid is an amino acid derivative. NCA method is based on the mechanism of anionic ring opening polymerization, which can be initiated by alkali. NCA reaction: under alkaline conditions, amino acid anions attack NCA to form carbamate ion. During acidification, the ion loses carbon dioxide to form dipeptides, and the dipeptides form anions to attack other NCAs under alkaline conditions. This process is repeated.
NCA method.
Combinatorial chemistry method: this method is based on the solid-phase peptide synthesis, that is, the amino acid construction units are connected by combination to synthesize a library containing a large number of compounds, and the compounds with the same physical and chemical properties or pharmacological activities are screened out. Combinatorial chemistry has great advantages in the discovery of drug precursors.
Liquid phase segmented synthesis method: this method is based on the characteristics that polypeptide fragments can be chemically and selectively linked together to grow polypeptides in solution. The commonly used joining techniques include natural chemical bonding, chemical regioselective bonding, removable auxilliary bonding, photosensitive auxilliary bonding, stoudinger joining, and orthogonal chemical bonding.
Natural chemical linking reaction.
2 biosynthesis
Biosynthesis mainly includes enzymolysis, genetic engineering and fermentation.
Enzymolysis: degradation of macromolecular animal or plant proteins by enzymes to obtain small molecular peptides. This method can not be industrialized because of low yield, long cycle and serious pollution. However, enzymatic hydrolysis can retain the nutritional value of the original protein, which is more green and healthy.
Genetic engineering method: this method is based on DNA recombination technology, which controls the generation of peptide sequence through DNA sequence. The advantages of this method are strong orientation, low cost, safety and health, but the yield is low and it is difficult to scale production.
Fermentation method: fermentation method is the use of microbial metabolism to obtain peptides. However, as far as we know, only cyanobacterial peptide, ε – PL and γ – PGA can be synthesized independently.
Application of polypeptide
Since the discovery and application of insulin in the 1920s, peptides have gradually become a research hotspot. More and more functional peptide molecules have been found and used in medicine, beauty, health care industry. Collagen polypeptide and antioxidant peptide of sheep placenta are used in skin care products and health care products, which can delay aging and protect skin and beauty. In medicine, peptides can serve human, animal and plant health as vaccines, drugs and diagnostic reagents.
Progress in research and development of peptide drugs in the world.
So far, more than 80 kinds of peptide drugs have been approved to enter the market, such as liraglutide, leuprorelin and other well-known products, and more than 400 kinds of drugs are in the stage of clinical research and development. Polypeptide drugs are effective in tumor, cardiovascular disease, diabetes, gastrointestinal disease, central nervous system disease, immune disease, antiviral and antibacterial, acromegaly.
Polypeptide drugs have many advantages, such as low side effects, strong specificity, high pharmacological activity, small dosage, less drug interaction, and environmental protection in the production process. However, polypeptide drugs also have some disadvantages, such as large-scale production difficulty, high research and development cost, complex purification work, poor metabolic stability, short half-life, difficult to pass the blood-brain barrier, and need injection.
In the future, the development of polypeptide drugs will focus on multi-functional peptide drugs, cell penetrating peptides, peptide coupling with other drugs, peptide vaccines, antimicrobial peptides and antiviral peptides.
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