Papain active cysteine

Peptide nitriles are reversible inhibitors of cysteine proteases. 1,2 Peptide nitrile reacts with the active site thiol group to form an imidothioate, a dead-end product that does not undergo hydrolysis to an amide.134 This imidothioate derivative has been detected by NMR spectroscopic studies.P 5 The inhibition of papain, a cysteine protease, by a peptide nitrile proved to be reversible in a dialysis experiment. 3 Peptide nitriles are weaker inhibitors of cysteine proteases than the corresponding aldehydes. 61 Most peptide nitriles show poor inhibition toward serine proteases, however those nitriles with proper peptide sequences are potent inhibitors of serine proteases. 7-9 ... 

Van der Hoorn RA, Leeuwenburgh MA, Bogyo M, Joosten MH, Peck SC (2004) Activity profiling of papain-like cysteine proteases in plants. Plant Physiol 135 1170-1178... 

Not only defense secondary metabolites but also defense proteins may exist as precursors. For example, papain, a cysteine proteinase that exists in papaya latex and recently found to have strong defense activity, is kept in laticifer as an inactive precursor and within 2 min after wounding, it becomes active.1 4... 

F .5.2 Inhibitors of papain family cysteine proteases. The heavy arrows indicate the direction of binding of the peptidal inhibitor relative to the active site cysteine thiol. The... 

Properties of cathepsin L may be compared among papain-like cysteine cathepsins (36-39) for understanding its role in producing neuropeptides. Cathepsin L belongs to the CIA subfamily of Clan CA (36). Clan CA was formed based on recognition of the first cysteine protease papain. The crystal structure of papain shows two structural domains separated by an active-site cleft. The N-terminal domain is comprised of a-helices, and the C-terminal domain contains a -barrel. 

Yuan F, Verhelst SH, Blum G, Coussens LM, Bogyo M. A selective activity-based probe for the papain family cysteine protease dipeptidyl peptidase Fcathepsin C. J. Am. Chem. Soc. 2006 128 5616-5617. 

Verhelst SH, Witte MD, Arastu-Kapur S, Fonovic M, Bogyo M. Novel aza peptide inhibitors and active-site probes of papain-family cysteine proteases. ChemBioChem 2006 7 943-950. 

The cystatins, which are a superfamily of proteins that inhibit papain-like cysteine proteases, are a classic example of these inhibitors. The cystatins (Fig. 3) insert a wedge-hke face of the inhibitor that consists of the protein N-terminus and two hairpin loops into the V-shaped active site of a cysteine protease. The N-terminal residues bind in the S3-S1 pockets in a substrate-like manner, but the peptide then turns away from the catalytic residues and out of the active site. The two hairpin loops bind to the prime side of the active site, which provides most of the binding energy for the interaction. Thus, both the prime and the nonprime sides of the active site are occupied, but no interactions are actually made with the catalytic machinery of the enzyme (23). 

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. 

For many years a controversy over the nature of papain activation confused the literature. Apparently cyanide, cysteine, glutathione, and... 

These reactions resemble a transacylation where the designed host has some of the properties of trypsin recognition of an NH3 group and papain (a cysteine residue at the active site). 

The detrimental effect of bleach should not be underestimated. Some enzymes like papain exhibit several valuable properties for laundering good thermal stability, low substrate specificity. In addition to its detrimental requirement of a low pH for maximum activity, papain contains cysteine residues, which must remain in the thiol form. In the presence of sodium perborate, they are oxidized and the enzyme activity is lost [15]. 

In each of two flasks place 15 ml of casein solution and 30 ml of water, adjust the temperature to 60° and place in a water-bath at 60°. To one flask add 5 ml of the solution of papain and cysteine hydrochloride and to the other add 5 ml of a portion of the same activated enzyme solution previously boiled for three minutes and cooled. Maintain both at 60° for thirty minutes. Cool rapidly to room temperature and to each flask add 0-75 ml of 0 1 per cent phenolphthalein solution and 10 ml of formaldehyde solution previously neutralised to phenolphthalein. Titrate both liquids with G IN sodium hydroxide to a definite pink colour (pH 8-7). The difference between the two titrations should not be less than 4-5 ml or more than 6-0 ml. 

Thus the alkaline protease obtained from Bacillus licheniformis with a molecular mass of about 27 000 consists of 274 amino acid residues and has serine and histidine as active sites. Pancreatic trypsin with a molecular mass of about 24 000 contains 230 amino acid residues and also has serine and histidine as active sites. Papain (molecular mass about 23 000 and 211 amino acid residues) has cysteine and histidine as active sites. 

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. 

N-Nitrosamines have been shown to be inhibitors of cysteine-containing enzymes. For example, dephostatin and other N-methyl-N-nitrosoanilines (1) were found to be inhibitors of the protein tyrosin phosphatases, papain and caspase [90,91]. Inhibition results from the S-nitrosation of the critical cysteine residues in the active sites of the enzymes by the nitrosamines. Compounds 6 and 7 have been found to inhibit thrombus formation in arterioles and venules of rats [92], while N-nitrosamide 9 exhibited vasodilation and mutagenicity as a result of NO release [93]. 

Cathepsin K (Cat K) is a member of the CA1 family of lysosomal cysteine proteases. This family is comprised of 11 human members (cathepsins B, C, F, H, K, L, O, S, V, W, Z) which share a common papain-like structural fold and a conserved active site Cys-Asn-His triad of residues [1-3]. These enzymes are synthesized as pre-pro-enzymes and are converted from the catalytically inactive zymogen into the active form in acidic lysosomal environment. In some cases, cathepsins are also secreted in the active form from cells. The sequence identity of... 

The first class of DUBs discovered, the ubiquitin C-terminal Aydrolases (UCHs), is a relatively small class vith only four members in humans and one in budding yeast. UCHs are cysteine proteases related to the papain family of cysteine proteases. Most UCHs consist entirely of a catalytic core that has a molecular mass of about 25 kDa, although Bapl and UCH37 have C-terminal extensions [21, 22], All UCHs have a highly conserved catalytic triad consisting of the active-site cysteine, histidine, and aspartate residues that are absolutely required for function [23]. 

The first and most extensively examined system was the hydrolytic enzyme papain. A variety of isomeric a-bromoacetylisoalloxazines were used to selectively tether a flavin moiety to the active site cysteine residue. Different isomeric linkages were proposed to allow orientations of the flavin relative to the substrate binding site which would favor reactions with a bound substrate [65]. 

The ability of coordinated NO to react with thiols has led to the suggestion of an alternative mechanism for activating guanylate cyclase. This involves nitroprusside oxidation of protein sulfhydryls to cross-link the protein with a disulfide bridge. For example, papain, which has an essential cysteine (cys-25) and glyceradehyde-3-phosphate dehydrogenase (cys-149) are both inhibited by nitroprusside with formation of [Fe(CN)5(NO)] and [Fe(CN)4NO] [132]. The suggested anaerobic reaction is ... 

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