Chymotrypsin-like Proteinases

Chymotrypsin-like proteinases are serine proteinases that recognize pqDtide residues with aromatic side chains (phyenylalanyl or tyrosyl residues) and that effect hydrolysis of the polypeptide chain on the carboxy-terminal side of these residues. Examples of chymotrypsin-like proteinases are chymotrypsin and cathepsin-G. 

Egelrud, T. and Lunstrom, A., A chymotrypsin-like proteinase that may be involved in desquamation in plantar stratum corneum, Ami . Dermatol. Res., 283, 108, 1991. 

Another difference between lipases and chymotrypsin-like proteinases is in the second H-bond to 082 of the catalytic aspartate. In chy-motrypsin the main-chain conformation of His-57 allows its amide group to provide the stabilizing H-bond, in contrast to lipases in which amides of Val-205 (RmL) and Thr-205 (hPL) serve a similar purpose. 

Choi, H.-K., et al. Structure of Sindbis virus core protein reveals a chymotrypsin-like serine proteinase and the organization of the virion. Nature 354 37-43, 1991. 

Tong, L., Wengler, G., and Rossmann, M. G. (1993). Refined structure of Sindbis virus core protein and comparison with other chymotrypsin-like serine proteinase structures. J. Mol Biol 230, 228-247. 

Sato, S. Shiratsuchi, A. (1990). Chymotrypsin-like zietivity of chicken liver multicataly tic proteinase resides in the smallest subunit. Biochim. Biophys. Acta, 1041, 2A9-71. 

A recent interesting article examined the effects of peptide aldehydes on a hepatitis A virus enzyme [232]. Picornaviral 3C proteinases are a group of closely related thiol proteinases responsible for processing viral polyprotein into its component proteins. These proteinases adopt a chymotrypsin-like fold [233, 234] and display an active site configuration similar to those of serine proteinases. The peptide aldehydes were based on the preferred peptide... 

Heidtmann HH, Travis J. A novel chymotrypsin-like serine proteinase from human lung. Biol Chem Hoppe Seyler 1993 374 871-875. 

Figure 2.19 Organization of polypeptide chains into domains. Small protein molecules like the epidermal growth factor, EGF, comprise only one domain. Others, like the serine proteinase chymotrypsin, are arranged in two domains that are required to form a functional unit (see Chapter 11). Many of the proteins that are involved in blood coagulation and fibrinolysis, such as urokinase, factor IX, and plasminogen, have long polypeptide chains that comprise different combinations of domains homologous to EGF and serine proteinases and, in addition, calcium-binding domains and Kringle domains.

Like SLPI, elafin is a very potent inhibitor of NE. Elafin interacts with elastase in a reversible manner and retains its inhibitory capacity upon dissociation of the complex. Kinetic data have shown that the association rate constant for the formation of an elafin-elastase complex is pH dependent [84]. Una is probably due to the bask properties of the inhibitor and enzyme. Elafin also inhibits proteinase 3 but has no effect on cathepsin G, trypsin, or chymotrypsin. This is inloestiitg in view of the fact that SLPI inhibits cathepsin G but la relatively ineffective against proteinase 3. 

Boronic acids (5a) were among the first examples of low-molecular-weight, reversible inhibitors of serine proteinases [151, 152]. Significant inhibition was initially demonstrated against a-chymotrypsin. Unlike the carbonyl-derived reversible inhibitors, which require a polypeptide or peptide-like chain, activity was found with simple alkylboronic acids (e.g. the value for PhCH2CH2B(OH)2 with a-chymotrypsin was = 40 //M) [153], Weak inhibition of elastase (PPE) was first reported for a series of arylboronic acids, for example, (10-1) [123]. Some of the boron-based inhibitors Figure 2.5) were tested as either the difluoroboranes (5b) or as the pinacol boronate esters (5c). These modifications were employed because they were more readily synthesized and/or purified than the boronic acids. For both of these derivatives inhibition was shown to be due to in situ hydrolysis to the parent boronic acid (5a) [154, 155]. 

Pepsin, pepsin-like enzymes, chymosin, rennin, and other acid proteinases have an activity optimum at pH 2.0-3.5 papain, trypsin, chymotrypsin, and similar enzymes are most active at neutral pH (pH 6-8). Subtilisin BPN, pancreatic elastase, leucine... 

A second elastolytic enzyme (Af, 21,900) has been isolated from porcine pancreas. It shows higher activity than chymotrypsin in the hydrolysis of acetyltyrosine ester, which is used routinely to assay chymotrypsin. Another E,-like enzyme, a-lytic proteinase (Af, 19,900, 198 amino acids) has been isolated from the soil bacterium Myxobacter 495. This enzyme is remarkably similar to pancreatic E. both in structure (41 % homology, sequence in the active center Gly-Asp-Ser-Gly, 3 homologous disulfide bridges) and substrate specificity. Another E. (Af, 22,300) has been isolated from Pseudomonas aeruginosa. 

Cathepsin G is an enzyme with dual chymotrypsin and trypsin-like specificity and as a leukocyte proteinase it is involved in the early stages of the immune response. Synthesis and inhibitory activity of a-aminoalkylpho-sphonates diphenyl esters as irreversible cathepsin G inhibitors has been described by Lesner et al. The phosphonates (244) and (245) turned out to be especially active. " ... 

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