Читать книгу Biomolecules from Natural Sources - Группа авторов - Страница 48

Most of organic compounds have applications that were successfully synthesized chemically after solving their structures. Even though the basic concept of the protein structure and composition was solved, proteins resist chemical synthesis, this is due mainly to its long variant polymeric chain. Proteins cannot be synthesized by organic chemists in large quantities and they cannot be manipulated in vitro to modify single amino acids in a protein and leave all other amino acids of that variety unchanged. However, the majority of proteins can be manipulated using in vivo genetic engineering. Once a gene coding for a protein has been cloned from the original wild-type genome into a vector it can be manipulated by using synthetic oligonucleotides to produce site specific mutations in the cloned material. This is specific and can alter any side chain of a particular amino acid to any other of the 20 naturally occurring amino acids. The technique of site-directed mutagenesis can alter any number of amino acids in a protein and can be used to build proteins from scratch. The position of the amino acid is decided by inspection of the tertiary structure of the primary structure (using conserved amino acids and site directed mutagenesis experiments) and the tertiary structure of the protein (using protein modeling), and the interaction of the amino acid with the substrate or with other parts of the main protein is evaluated mathematically. Conserved amino acids can be determined from the protein primary structure using alignment. Conserved amino acids are usually responsible for important functions. It is, of course, necessary to have a reasonable idea of what property one is trying to enhance in the target protein. Wrong manipulation of protein could lead to fatal problems. Proteins produced through biological systems (genetically unmodified protein) are the safest choice [57, 97, 98].

There are many concepts controlling the uses of protein in medicinal applications such as is purity. In technical applications (e.g., technical enzyme) the boundaries of purity are different. Regarding activity and stability, the protein must match perfectly the purpose of its use. The importance of protein engineering in industry continues to grow as the number of applications of proteins expands, and the technology used to discover proteins efficiently with useful properties is better able to address industrially relevant problems. Recent advances in directed evolution are implemented in many established industrial laboratories as well as in start-up companies, augmenting the rational design approach. Additionally, organisms from extreme environments are becoming an important source of new backbones for engineering proteins with significantly different properties. The successfully engineered protein generally requires a proper combination of properties. For example, a detergent protease would require, at minimum, stability in the presence of detergent and activity against certain protein stains. Nevertheless, the control of a few basic properties is a recurring theme in many applications. Properties such as sufficient stability, high activity (in the case of enzymes), and the ability to interact correctly with surfaces are necessary for a variety of industrially important proteins [99].