Enzymes serin protease

Several pharmaceutical enzymes belong to the group of serine-histidine estero-proteolytic enzymes (serine proteases), which display their catalytic activity with the aid of an especially reactive serine residue, whoso p-hydroxyi group forms a covalent bond with the substrate molecule. This reaction takes place by cooperation with the imidazole base of histidine. The specificity of the enzymes is achieved by the characteristic strocture of their substrate-binding centers, which in these proteases are built according to the same principle. They consist of a hydrophobic slit formed by apolar aide chains of amino acids and a dissociated side chain-located carboxyl group of an aspartic add residue at the bottom. 

Many enzymes have been the subject of protein engineering studies, including several that are important in medicine and industry, eg, lysozyme, trypsin, and cytochrome P450. SubtiHsin, a bacterial serine protease used in detergents, foods, and the manufacture of leather goods, has been particularly well studied (68). This emphasis is in part owing to the wealth of stmctural and mechanistic information that is available for this enzyme. 

Engineering Substrate Specificity. Although the serine proteases use a common catalytic mechanism, the enzymes have a wide variety of substrate specificities. For example, the natural variant subtiHsins of B. amyloliquefaciens (subtiHsin BPN J and B. licheniformis (subtiHsin Carlsberg) possess very similar stmctures and sequences where 86 of 275 amino acids are identical, but have different catalytic efficiencies, toward tetraamino acid -nitroanilide substrates (67). 

An example of a pseudoirreversible inhibitor has been demonstrated for chymotrypsin (36). This enzyme is a serine protease, and its mechanism of catalysis may be outlined as follows, where or R2 preferentially is a hydrophobic amino acid residue. 

Smith, S.O., et al. Crystal versus solution structures of enzymes NMR spectroscopy of a crystalline serine protease. Science 244 961-964, 1989. 

FIGURE 16.26 Acyl-enzyme and amino-enzyme intermediates originally proposed for aspartic proteases were modeled after the acyl-enzyme intermediate of the serine proteases. 

According to their genetic relationship and their biochemical mechanism of action (3-lactamases are divided into enzymes of the serine-protease type containing an active-site serine (molecular class A, C, and D enzymes) and those of the metallo-protease type (molecular class B enzymes), which contain a complex bound zinc ion. 

Antibiotic Resistance. Figure 1 According to Bush, Jacoby and Medeiros [2] four molecular classes of (3-lactamases can be discriminated based upon biochemical and molecular features. Classes 1, 2, and 4 included serine-proteases, while metallo enzymes are included in class 3. The substrate spectrum varies between different subclasses and the corresponding genes can be part of an R-plasmid leading to a wider distribution or are encoded chromosomally in cells of specific species. 

Fibrin is formed from fibrinogen synthesized by the liver and secreted into the circulation. The conversion of fibrinogen to fibrin is initiated by a serine protease, thrombin. Thrombin, at the same time, can activate a transglutaminase enzyme, factor XIII present in... 

Furin, also known as paired basic amino-acid-cleaving enzyme (PACE), is a membrane bound subtilisin-like serine protease of the irons Golgi compartment. It is ubiquitously expressed and mediates processing of many protein precursors at Arg-X-Lys/Arg-Arg sites. 

The serine proteases are the most extensively studied class of enzymes. These enzymes are characterized by the presence of a unique serine amino acid. Two major evolutionary families are presented in this class. The bacterial protease subtilisin and the trypsin family, which includes the enzymes trypsin, chymotrypsin, elastase as well as thrombin, plasmin, and others involved in a diverse range of cellular functions including digestion, blood clotting, hormone production, and complement activation. The trypsin family catalyzes the reaction ... 

SCF, see Self-consistent field treatment (SCF) Schroedinger equation, 2,4,74 Secular equations, 6,10, 52 solution by matrix diagonalization, 11 computer program for, 31-33 Self-consistent field treatment (SCF), of molecular orbitals, 28 Serine, structure of, 110 Serine proteases, 170-188. See also Subtilisin Trypsin enzyme family comparison of mechanisms for, 182-184, 183... 

Structural analysis of the rhinovirus and the hepatitis A virus 3C proteases (Allaire et al. 1994 Matthews et al. 1994) confirmed earlier predictions that the picomavirus 3C proteases are similar to chymotrypsin-Uke serine proteases in their fold. An important difference is that the serine nucleophile of serine proteases is replaced with a cysteine however, the 3C protease is stracturally distinct from the eukaryotic cysteine protease class of enzymes. 

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