Читать книгу Biomolecules from Natural Sources - Группа авторов - Страница 47

The word protein comes from the Greek word πρώτειος (proteios) “primary”. Proteins were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838. However, the involvement of proteins in living system organisms was correctly understood in 1926, when James B. Sumner showed that urease was a protein defined by the sequence of its related nucleotides and amino acids [56]. The genetic code can include selenocysteine and in certain cases (such as in archaea) pyrrolysine. The residues in a protein are often observed to be chemically modified by post-translational modification, which can happen either before the protein is used in the cell, or as a part of control mechanisms. Proteins can also work together to achieve a particular function, and they often associate to form stable complex functions, such as actin and myosin in muscles and proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle [57].

Proteins are natural chains of amino acids joined by amide linkages. They are degraded by enzymes (proteases). For thousands of years people used natural proteins such as wool [58], silk [45] and hair (keratin) for clothes, decoration or to display their wealth. After understanding their composition, they were reformulated and their properties changed to match certain demands. Numerous proteins were studied for developing natural bio-based materials such as keratin, collagen, albumin, gelatin, and fibroin [59]. They are degraded by enzymes. Nowaday some old techniques are still used to produce products from some types protein–polymer such as wool [60], silk [61–64], and hair [65–67]. However, some modern applications have been invented such as the use of Keratin [68–70] in hydrogel. Silk is used in tissue engineering, in drug delivery for musculoskeletal therapeutics. The first industrial applications of protein as polymer were in the early 1930s and 1940s with casein and with soy protein. Protein biopolymers can be classified with animal proteins (e.g. casein [71–75], whey [76–79], keratin [58, 68, 80, 81], collagen [82–85] and gelatine [86], polyglutamic) and in plant proteins (wheat, corn, soy, pea and potato proteins) and microbial protein such as polyglutamic [87–89], cyanophycin [90–93] protein biopolymers remained present in some niche markets such as encapsulates (pharmaceutical), coatings (food industry), adhesives or surfactants. They are used in the packaging industry for breweries, wineries and essential oil composite film for refrigerated products; microcapsules based on biodegradable polymers [72, 90, 93]. Protein biopolymers remain in some niche markets such as encapsulates (pharmaceutical), coatings (food industry), adhesives or surfactants. They are used in the packaging industry for breweries, wineries and refrigerated products essential oil composite film, microcapsules based on biodegradable polymers [57, 72].

Mammalians are not able to produce all 20 amino acids (essential amino acids). They obtain those essential amino acids through their diet. The first protein to be fully sequenced was insulin, by Frederick Sanger, who won the Nobel Prize for this achievement in 1958. It is important to highlight that Sanger succeed in solving the insulin sequence using insulin itself rather using the related genes. It was a complicated process especially in the presence of the disulfide bond between A and B fragments. Sanger discovered early the importance of the 3D structure of the protein. The first protein structures to be solved using data obtained from x-ray diffraction analysis included hemoglobin and myoglobin, by Max Perutz and Sir John Cowdery Kendrew, respectively, in 1958 [94, 95]. The 3D structures of both proteins were determined; Perutz and Kendrew shared the 1962 Nobel Prize in Chemistry for these discoveries. Rapid advances in site-directed mutagenesis and total gene synthesis combined with new expression systems in prokaryotic and eukaryotic cells have provided the molecular biologist with tools for modification of existing proteins to improve catalytic activity, stability and selectivity, for construction of chimeric molecules and for synthesis of completely novel molecules that may be endowed with some useful activity. The results are used in the improvement of the design by using knowledge-based procedures that exploit facts, rules and observations about proteins of known 3D structure [96].