21-Amino acid polypeptide

Figure 16.17 The subunit structure of the bacteriophage MS2 coat protein is different from those of other sphericai viruses. The 129 amino acid polypeptide chain is folded into an up-and-down antiparallei P sheet of five strands, P3-P7, with a hairpin at the amino end and two C-terminai a helices. (Adapted from a diagram provided by L. Liijas.)...

Lysozyme from bacteriophage T4 is a 164 amino acid polypeptide chain that folds into two domains (Figure 17.3) There are no disulfide bridges the two cysteine residues in the amino acid sequence, Cys 54 and Cys 97, are far apart in the folded structure. The stability of both the wild-type and mutant proteins is expressed as the melting temperature, Tm, which is the temperature at which 50% of the enzyme is inactivated during reversible beat denat-uration. For the wild-type T4 lysozyme the Tm is 41.9 °C. 

ADH Horse liver alcohol dehydrogenase, an enzyme dimer of identical 374 amino acid polypeptide chains. The amino acid composition of ADH is reasonably representative of die norm for water-solnble proteins. 

PTH is the most important regulator of bone remodelling and calcium homeostasis. PTH is an 84-amino acid polypeptide and is secreted by the parathyroid glands in response to reductions in blood levels of ionised calcium. The primary physiological effect of PTH is to increase serum calcium. To this aim, PTH acts on the kidney to decrease urine calcium, increase mine phosphate, and increase the conversion of 25-OH-vitamin D to l,25-(OH)2-vitamin D. PTH acts on bone acutely to increase bone resorption and thus release skeletal calcium into the circulation. However, due to the coupling of bone resorption and bone formation, the longer-term effect of increased PTH secretion is to increase both bone resorption and bone formation. 

Sela, M., Synthetic antigens and recent progi ss in immunology, in Peptides. Polypeptides and Proteins. Proceedings of the Rehovot Symposium on Poly (Amino Acids), Polypeptides and Proteins, John Wiley and sons, New York, 1974, pp. 495-509... 

Methodologies for the de novo design and synthesis of polypeptides were recently developed. The preparation of periodic polypeptides, polypeptides containing artificial amino acids, polypeptides exhibiting rodlike structures, and hybrids of natural and artificial polypeptide segments was recently described [33],... 

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) are members of a family of so-called natriuretic peptides, synthesized predominantly in the cardiac atrium, ventricle, and vascular endothelial cells, respectively (G13, Y2). ANP is a 28-amino-acid polypeptide hormone released into the circulation in response to atrial stretch (L3). ANP acts (Fig. 8) on the kidney to increase sodium excretion and glomerular filtration rate (GFR), to antagonize renal vasoconstriction, and to inhibit renin secretion (Ml). In the cardiovascular system, ANP antagonizes vasoconstriction and shifts fluid from the intravascular to the interstitial compartment (G14). In the adrenal cortex, ANP is a powerful inhibitor of aldosterone synthesis (E6, N3). At the hypothalamic level, ANP inhibits vasopressin secretion (S3). It has been shown that some of the effects of ANP are mediated via a newly discovered hormone, called adreno-medullin, controlling fluid and electrolyte homeostasis (S8). The diuretic and blood pressure-lowering effect of ANP may be partially due to adrenomedullin (V5). 

IL-ll is a 23 kDa, 178 amino acid polypeptide. Its receptor appears to be a single-chain 150 kDa transmembrane protein. Binding of IL-ll results in tyrosine phosphorylation of several intracellular proteins, which, in turn, somehow promote the observed biological activities of IL-ll. 

Human TNF-a is initially synthesized as a 233 amino acid polypeptide that is anchored in the plasma membrane by a single membrane-spanning sequence. This TNF pro-peptide, which itself displays biological activity, is usually proteolytically processed by a specific extracellular metallo-protease. Proteolytic cleavage occurs between residues 76 (Ala) and 77 (Val), yielding the mature (soluble) 157 amino acid TNF-a polypeptide. Mature human TNF-a appears to be devoid of a carbohydrate component, and contains a single disulfide bond. 

Insulin was first identified as an anti-diabetic factor in 1921, and was introduced clinically the following year. Its complete amino acid sequence was determined in 1951. Although mature insulin is a dimeric structure, it is synthesized as a single polypeptide precursor, i.e. preproinsulin. This 108 amino acid polypeptide contains a 23 amino acid signal sequence at its amino terminal end. This guides it through the endoplasmic reticulum membrane, where the signal sequence is removed by a specific peptidase. 

Human parathyroid hormone (hPTH) is an 84 amino acid polypeptide that functions as a primary regulator of calcium and phosphate metabolism in bones. It stimulates bone formation by osteoblasts, which display high-affinity cell surface receptors for the hormone. PTH also increases intestinal absorption of calcium. 

Purification entails use of an immunoaffinity column containing immobilized murine antifactor VII antibody. It is initially produced as an unactivated, single-chain 406 amino acid polypeptide, which is subsequently proteolytically converted into the two-chain active factor Vila complex. After sterilization by filtration, the final product is aseptically filled into its final product containers, and freeze-dried. 

The presence of an anticoagulant in the saliva of the leech, Hirudo medicinalis, was first described in 1884. However, it was not until 1957 that the major anticoagulant activity present was purified and named hirudin. Hirudin is a short (65 amino acid) polypeptide, of molecular mass 7000 Da. The tyrosine residue at position 63 is unusual in that it contains a sulfate group. The molecule appears to have two domains. The globular N-terminal domain is stabilized by three disulfide linkages, whereas the C-terminal domain is more elongated and exhibits a high content of acidic amino acids. 

Papain is a cysteine protease isolated from the latex of the immature fruit and leaves of the plant Carica papaya. It consists of a single 23.4 kDa, 212 amino acid polypeptide, and the purified enzyme exhibits broad proteolytic activity. Although it can be used as a debriding agent, it is also used for a variety of other industrial processes, including meat tenderizing and for the clarification of beverages. 

Parathyroid hormone (PTH) regulates calcium levels in blood and bone remodeling. The activation domain of that 84-amino acid polypeptide locates around the N-terminal (1-34 amino acids). Parathyroid hormone receptor is a typical G-protein coupled receptor, which is coupled to both adenyl cyclase/cAMP and PLCy/IP3/cytosolic Ca2+ intracellular signaling pathways. In order to identify the structural elements involved in the peptide hormone binding and signal initiation, Chorev et al. employed a photoaffinity scanning approach. The N-terminal amino acids were successively deleted or modified and the new N-terminus was replaced for photoreactive Bpa. The most active peptide ana-... 

Theoretically, any number of solutes can be separated in this manner and the method has been applied, for example, to the separation of fatty acids, amino acids, polypeptides and other biological materials with distribution... 

Tumor Necrosis Factor There are two types of tumor necrosis factor TNF-a and TNF- 8. Of the two, TNF-a has been studied in more detail. TNF-a is a 157 amino acid polypeptide. It is a mediator of immune regulation, including the activation of macrophages and induction of the proliferation of T cells. Another TNF-a function is its cytotoxic effects on a number of tumor cells. Recent research, however, concentrates on its property in the stimulation of inflammation, particularly in the case of rheumatoid arthritis. Clinical trials are being conducted with drugs to block TNF-a with anti-TNF-a monoclonal antibodies. These antibodies target the excessive levels of TNF-a in the synovial fluid of joints and provide relief to sufferers of rheumatoid arthritis (Exhibit 4.10). 

Infrared Analysis of the Structure of Amino Acids, Polypeptides, and Proteins... 

TGF-a is initially synthesized as an integral membrane protein. Proteolytic cleavage releases the soluble growth faetor, which is a 50 amino acid polypeptide. This growth factor exhibits a high... 

Purification entails use of an immunoaffinity column containing immobilized murine antifactor VII antibody. It is initially produced as an unactivated, single chain 406 amino acid polypeptide, which is subsequently proteolytically converted into the two-chain active factor Vila complex. After sterilization by filtration, the final product is aseptically filled into its final product containers and freeze-dried. The excipients present in the product include sodium chloride, calcium chloride, polysorbate 80, mannitol and glycylglycine. When freeze-dried in the presence of these stabilizing substances and stored under refrigerated conditions, the product displays a shelf-life of at least 2 years. It has proved effective in the treatment of serious bleeding events in patients displaying anti-factor VIII or IX antibodies. 

Calcitonin (Miacalcin, Miacalcin Nasal Spray) is a synthetic 32-amino acid polypeptide that is identical to salmon calcitonin. Salmon calcitonin is more potent than human calcitonin because of its higher affinity for the human calcitonin receptor and its slower metabolic clearance. Administration is by subcutaneous or intramuscular injection or by nasal spray. The absorption of the nasal form is slower than that of the parenteral routes. 

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