Protease catalyzed hydrolysis

The most recent advance in treating HIV infections has been to simultaneously attack the virus on a second front using a protease inhibitor. Recall from Section 27.10 that proteases are enzymes that catalyze the hydrolysis of proteins at specific points. When HIV uses a cell s DNA to synthesize its own proteins, the initial product is a long polypeptide that contains several different proteins joined together. To be useful, the individual proteins must be separated from the aggregate by protease-catalyzed hydrolysis of peptide bonds. Protease inhibitors prevent this hydrolysis and, in combination with reverse transcriptase inhibitors, slow the reproduction of HIV. Dramatic reductions in the viral load in HIV-infected patients have been achieved with this approach. 

Figure 6. (a) Tetrahedral intermediate formed during aspartyl protease-catalyzed hydrolysis and (b) the( S)- and (R)-hydroxyethylamine-based isosteres. 

Swann, P. G. Casanova, R. A. Desai, A. Frauenhoff, M. M. Urbancic, M. Slomczynska, U. Hopfmger, A. J. Le Breton, G. C. Venton, D. L. Nonspecific protease-catalyzed hydrolysis/synthesis of a mixture of peptides Product diversity and ligand amplification by a molecular trap. Biopolymers 1997, 40, 617-625. 

Swann PG, Casanova RA, Desai, A, Erauenhoff MM, Urbancic M, Slomczynska U, Hopfinger AJ, LeBreton GC, Venton DL. Nonspecific protease-catalyzed hydrolysis synthesis of a... 

Capelo, J.L., P. Ximenez-Embun, Y. Madrid-Albarran, and C. Camara. 2004. Enzymatic probe sonica-tion Enhancement of protease-catalyzed hydrolysis of selenium bound to proteins in yeast. Anal. Chem. 76 233-237. 

Synthetic peptide inhibitors have been developed for a variety of proteases [199-204]. Peptide inhibitors of the metalloprotease angiotensin I converting enzyme (ACE) are of major importance as hypertensive agents [13, 31]. A variety of peptides derived from protease-catalyzed hydrolysis of com cc-zein [202-203] or of wheat germ protein [199, 204] inhibit ACE (Table 6). The most potent of such plant-derived ACE inhibitory peptides is Ile-Val-Tyr (IVY) (Ki 0.1 xM) [199, 204], Further plant-derived peptide ACE inhibitors include the tripeptide glutathione [73, 82], the glutathione -related peptide Y-L-glutamyl-(+)-allyl-L-cysteine sulphoxide [73, 82, 200, 201] and the tripeptide His-His-Leu (HHL) from fermented soybean [201] (Table 6). 

The role of catalysis in membrane assembly is emphasized again by the above model since the N-terminal sequence of the nascent polypeptide chain of a spanning protein is released by proteolysis as soon as it reaches the cytosol. The N-terminal polypeptide chain extension may help the chain penetrate the hydrophobic bilayer and solubilize the resulting hydrophobic N-terminal part of the chain in the aqueous medium of the cytoplasm. However, the role of the protease-catalyzed hydrolysis of the polypeptide chain in membrane assembly is minimized in the membrane trigger hypothesis (99). According to this model, the essential role of the leader sequence would be to modify, in association with the lipid bilayer, the folding pathway of the protein in such a way that the polypeptide chain could span the membrane. 

Rather interesting conclusions can be drawn from an examination of the serine protease-catalyzed hydrolysis of a series of esters or anilides of basic substituted benzoic acids and amidinophenyl esters of aromatic carboxylic acids [1-10]. They react with the serine proteases like a substrate by acylation of the serine residue of the active center and by simultaneous release of the alcoholic... 

This modification seems to mimic the presumed tetrahedral intermediate involved in the aspartyl protease-catalyzed hydrolysis of the peptide bond. A HIV-1 protease inhibitor containing a hydroxyethylene bond isostere has been prepared on solid phase [143]. A Boc-N-protected bromomethyl ketone was coupled to the resin-bound N-free Pro-Ile-Val tripeptide, and the keto function was reduced to an OH group with NaBH4.The peptide analogue was then elongated on the resin.This procedure allows rapid access to a variety of hydroxyethylamino peptide bond isosteres, and in good yield. 

Tam JP, Lu Y, Liu CF et al. (1995) Peptide synthesis using unprotected peptides through orthogonal coupling methods. Proc Natl Acad Sci USA 92(26) 12485-12489 Thormann M, Thurst S, Hofmann H et al. (1999) Protease-catalyzed hydrolysis of substrate mimet-ics (inverse substrates) a new approach reveals a new mechanism. Biochemistry 38(19) 6056-6062... 

An elegant example of a protease-catalyzed hydrolysis of a carboxylic ester was demonstrated by the dynamic resolution of the antiinflammatory agent ketorolac via hydrolysis of its ethyl ester by an alkali-stable protease derived from... 

The peptide acids generated by protease-catalyzed hydrolysis of proteins are generally good inhibitors of the enzymes that produce them. In the past few years it has become clear that derivatives of peptide acids in which the carboxylic acid group has been replaced by an aldehyde group are even more potent inhibitors of certain proteases than are the... 

Proteases for peptide synthesis are selected on the basis of their specificity against amino acid residues and include the majority of the commercially available proteases of the four classes mentioned above [58]. Protease-catalyzed bond synthesis can be carried out either as an equilibrium-controlled process which is the direct reversal of the protease-catalyzed hydrolysis or a kinetically controlled process. In the latter case weakly activated carboxy components are employed [61]. 

Proteases catalyze hydrolysis of peptide (amide) bonds... 

Serine and cysteine protease-catalyzed hydrolysis of esters and amides involves two steps (1) attack of the active site nucleophile on the carbonyl at the cleavage site to form an acyl-enzyme intermediate, and (2) hydrolysis of the acylated enzyme to regenerate the catalyst (Equation 1). We wondered whether a selenol group (-SeH) could assume the role of the active site nucleophile. We found that selenolsubtilisin, like thiolsubtilisin, is a poor amidase. Thus, i F-succinyl-Ala-Ala-Pro-Phe-p-nitro-anilide is not hydrolyzed at all by the selenol-containing enzyme even though it is an excellent substrate for subtilisin itself. Activated esters, on the other hand, are substrates. 

Lipases and esterases typically show selectivity toward the alcohol or amine part of a carboxylic acid derivative. Favored acyl groups are simple straight chains like acetate or butyrate. In contrast, proteases show higher specificity for the acyl part of a carboxylic acid derivative. Proteases contain a specificity pocket for the acyl group. For example, subtilisins and chymotrypsin favor ester and amides of phenylalanine esters. Another difference between the enzyme classes is that lipases and esterases catalyze hydrolysis of only esters, whereas proteases catalyze hydrolysis of both amides and esters. Several good books on hydrolases in organic synthesis are available [2-4]. 

KINETIC RESOLUTION OF P-TOLYLSULFINAMIDE BY PROTEASE-CATALYZED HYDROLYSIS OF THE N-3-(3-PYRIDINE)PR0PI0NYL AMIDE... 

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