Proteases classes

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. 

The unsaturated residues Dha and Dhb are formed by dehydration of serine and threonine residues, respectively, and the thioether linkages Lan and MeLan are generated by intramolecular Michael-type addition of cysteine thiols to the unsaturated sites (e.g., Fig. 3b). These modifications can be performed by either two separate enzymes (LanB and LanC) in class I lantibiotics or a single bifunctional enzyme (LanM) in class II lantibiotics. Typically, proteolysis of the leader sequence is performed by a dedicated protease, either a LanP serine protease (class I) or the cysteine protease domain of a LanT protein (class II). The lanB genes encode large ( 1000 residues) predominantly hydrophilic dehydratases that may be membrane associated. To date, the dehydratase activity of a LanB protein has not been reconstituted in vitro and little is known about the mechanism of catalysis of this group of enzymes. 

None of the protein inhibitors of NE presented in this chapter are protease specific. They all inhibit more than one protease, but they are protease class specific (Table 5). For example, ai-PI, SLPI, and eglin c are serine-protease inhibitors and inhibit trypsin, chymotrypsin, and cathepsin G in addition to NE. However, ai-PI is an inhibitor of neutrophil PR3, whereas SLPI and eglin c are only very weak inhibitors of PR3 [40]. By contrast, elafin, which shares 38% homology with the C-terminal domain of SLPI, does inhibit PR3. A strong selectivity for NE is important to reduce toxicity resulting from interference of the inhibitor with other proteolytic processes. 

Protease Inhibitor Protease Class Working Concentration Special Characteristics... 

Chymotrypsin is a member of the serine protease class of enzymes. Its mechanism of action is described in Section 24.11. Using the information presented there (and pierhaps supplemented by information from a biochemistry textbook), prepare notes for a class presentation on the mechanism of chymotrypsin. Consider especially the role of the catalytic triad with r ard to acid—base catalysis and the relative propensity of various groups to act as nucleophiles or leaving groups. 

Rhizopus pepsin belongs to the aspartyl protease family, whose members are distributed in microorganisms, plants, and animals. This protease class cleaves peptide bonds on the N-terminal side of Phe or Tyr. 

The alignment of them realized in the tetrapetide allows for a simultaneous inhibition of the proteolytic activity of trypsin-like serine proteases, papain-like cysteine proteases, and pepsin-like aspartyl proteases. Therefore, this unique compound represents a blueprint for the design of protease class-spanning inhibitors [85, 86]. The capability of (59) to inhibit proteases belonging to different classes for trypsin, cathepsin B, cathepsin L, and papain was reported (see Table 30.3). Miraziridine A [85] also inhibited cathepsin B with an IC50 value of 1.4 pg/mL. Aziridine-2,3-dicarboxylic acid (14) is a rare natural product, reported from a Streptomyces [36], and vArg has never before reported as a natural product. 

Schaschke, N. (2004) Miraziridine A natures blueprint towards protease class-spanning inhibitors. Bioorg. Med. Chem. Lett., 14, 855-857. 

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. 

Apart from these two Vertex compounds, only one other caspase inhibitor, BDN-6556, has been used in clinical trials. This compound belongs to the class of oxamyl dipeptides and was originally developed by Idun Pharmaceuticals (taken over by Pfizer). It is the only pan-caspase inhibitor that has been evaluated in humans. BDN-6556 displays inhibitory activity against all tested human caspases. It is also an irreversible, caspase-specific inhibitor that does not inhibit other major classes of proteases, or other enzymes or receptors. The therapeutic potential of BDN-6556 was first evaluated in several animal models of liver disease because numerous publications suggested that apoptosis contributes substantially to the development of some hepatic diseases, such as alcoholic hepatitis, hepatitis B and C (HBV, HCV), non-alcoholic steato-hepatitis (NASH), and ischemia/reperfusion injury associated with liver transplant. Accordingly, BDN-6556 was tested in a phase I study. The drug was safe and... 

ET-1 from big-ET-1 by other proteases such as neutral endopeptidase or other currently unidentified proteases. Therefore, dual inhibition of ECE and NEP might inhibit ET-l generation more efficiently, than that seen for selective ECE inhibitors. However, dual inhibiton of ECE and NEP could also increase the risk for the development of AD, as both enzyme classes are involved in the degradation of A 3 peptide. 

So far, five different protease inhibitors have been approved by the FDA for the treatment of HIV infection [3, 4]. Clinical trials in which protease inhibitors were evaluated in monotherapy demonstrated the potency of this class of inhibitors (decrease in HIV RNA levels, increase in CD4 cell counts). Treatment regimens were subsequently broadened to include reverse transcriptase inhibitors in combination with protease inhibitors. The result of these clinical trials has led to a list of guidelines with recommendations for the optimal treatment options. Prolonged control of the infection with combination therapy (highly active antiretroviral therapy, HAART ) could be shown. 

Amprenavir (APV, Agenerase) is the most recently approved HIV protease inhibitor. It is smaller and stereochemically less complex than the other drugs in this class. Adsorption of this compound was found to be impaired by high fat meals. Common side effects of Amprenavir are nausea, vomiting, diarrhea, rash and a tingling sensation around the mouth. 

As with reverse transcriptase inhibitors, resistance to protease inhibitors may also occur. Mutations in the HIV protease gene were shown to confer resistance to each of the aforementioned molecules. In addition, passaging of viius in the presence of HIV protease inhibitors also gave rise to strains less susceptible to the original inhibitor or cross-reactive to other compounds in the same class. New Diug Targets... 

Rhinoviruses, which represent the single major cause of common cold, belong to the family of picornavimses that harbors many medically relevant pathogens. Inhibitors of the 3C protease, a cysteine protease, have shown good antiviral potential. Several classes of compounds were designed based on the known substrate specificity of the enzyme. Mechanism-based, irreversible Michael-acceptors were shown to be both potent inhibitors of the purified enzyme and to have antiviral activity in infected cells. 

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 ... 

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