The future belongs to synthetic antibodies
Antibodies are a weapon of the immune system that neutralizes pathogens and promotes their elimination from the body. Antibodies produced in laboratory conditions are widely used in biomedical research, as well as in the diagnosis and treatment of a number of human diseases. However, modern methods of antibody production are very complex and costly, which ensures an exceptionally high cost of the final product.
Researchers at the Biodesign Institute, part of Arizona State University, working under the leadership of Stephen Albert Johnston, have developed a much faster and simpler method of antibody synthesis, the secret of which lies in carrying out the stages of the traditional method in reverse order. Another important advantage of artificial antibodies that distinguishes them favorably from biological analogues is their exceptional stability, which makes these antibodies an ideal component of diagnostic kits.
Traditionally, the production of antibodies begins with the synthesis of a protein that the antibodies should bind to. This protein is injected into the body of an animal (mouse, rabbit, etc.), which reacts by triggering the synthesis of antibodies. After that, the animal is killed and antibodies are isolated directly from its body or the B-lymphocytes producing them (usually mouse) are hybridized with the cells of a human tumor – myeloma. The resulting culture of chimeric cells – a hybrid – lives relatively well in culture and produces so-called monoclonal antibodies.
The authors suggest starting the antibody production process "from the end", that is, with the chemical synthesis of antibodies directly. To do this, peptides are synthesized from amino acids, which are subsequently connected in pairs using a chemical framework. The resulting artificial antibodies are tested for their ability to bind to a variety of human proteins.
This strategy is based on the fact that the binding strength of a complex of two amino acid chains with a target protein is determined by the affinity (chemical affinity with this protein) of both chains. In other words, combining two peptides with weak affinity makes it possible to obtain an antibody that binds strongly to a certain protein. It is worth noting the fact that both the assembly of individual peptides and their combination into a synthetic antibody (synbody, from synthetic + antibody) occur randomly.
The raw material for the production of artificial antibodies is a library containing 10,000 peptides whose amino acid sequences are randomly composed. According to Johnston, the principle of randomness is a key aspect of the entire strategy. He explains this by the fact that sequences of randomly combined amino acids are more plastic than those that are part of living organisms. Each of the linear peptides contained in the library theoretically has two or three fragments for interaction with almost any protein. The combination of two such peptides leads to the formation of a ligand that demonstrates a high degree of affinity for a particular protein.
To date, the only technological limitation of the method is the number of proteins applied to one slide when testing artificial antibodies, but Johnston notes that this aspect is being improved very quickly. The results obtained by testing the interaction of antibodies with numerous proteins are used to create a library of effective ligands. The ability to synthesize antibodies to the entire proteome of the human body, which includes about 30,000 proteins, will allow not only to study in detail the functioning of these proteins, but also to develop a huge number of new diagnostic tests.
To create artificial antibodies to a specific protein, for example, associated with a disease, it is possible to analyze the ability of this protein to bind to various peptides from the available library. Identification of two suitable peptides will allow synthesizing the necessary antibody. This approach is effective, but requires a lot of time.
To date, the authors have managed to synthesize artificial antibodies capable of firmly binding the AKT-1 protein associated with aging, obesity and malignant diseases. They believe that the methodology they have developed has a great future both in biomedical science and in practical medicine.
The results of the work are published in the journal PLoS ONE in the article "Discovery of High-Affinity Protein Binding Ligands – Backwards".
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru Based on ScienceDaily: Artificial Antibodies Hold Biomedical Promise.
31.05.2010