Threonine proteases

Powers, J. C. Asgian, J. L. Dogan Ekici, O. Ellis James, K. Irreversible inhibitors of serine, cysteine, and threonine proteases. Chem. Rev. 2002, 102, 4639 -750. 

E. Seemiiller, A. Lupas, D. Stock, J. Lowe, R. Huber, W. Baumeister, Proteasome from Thermoplasma Acidophilum A Threonine Protease , Science 1995, 268, 579-582. 

The catalytic core of the proteasome is a threonine protease. Based on the crystal structure of the proteasome, it was concluded that proteasome functions through a new kind of proteolytic mechanism. In... 

Proteases are enzymes that cleave proteins by hydrolyzing peptide bonds. On the basis of their catalytic mechanisms, they can be classified into five main types proteases that have an activated cysteine residue (cysteine proteases), an activated aspartate (aspartate proteases), a metal ion (metalloproteases), or an activated threonine (threonine proteases), and proteases with an active serine (serine proteases). Within each type, enzymes are separated into clans (also referred to as superfamilies ) based on evidence of evolutionary relationship [60, 61] from the linear order of... 

Proteases are enzymes catalyzing the hydrolysis of peptide bonds. They form one of the largest enzyme families encoded by the human genome, with more than 500 active members. Based on the different catalytic mechanisms of substrate hydrolysis, these enzymes are divided into four major classes serine/threonine, cysteine, metallo, and aspartic proteases. In serine, cysteine, and threonine proteases, the nucleophile of the catalytic site is a side chain of an amino acid in the protease (covalent catalysis). In metallo and aspartic proteases, the nucleophile is a water molecule activated through the interaction with amino acid side chains in the catalytic site (non-covalent catalysis) (Gerhartz et al., 2002). 

Figure 1 Diagram of a protease active site. A protease cieaves a peptide at the scissiie bond, and has a number of specificity subsites, which determine protease specificity. Substrates bind to a protease with their non-prime residues on the N-terminai side of the scissiie bond and their prime-side residues C-terminal to the scissiie bond. The cataiytic residues determine the ciass of protease. Serine, cysteine, and threonine proteases hydroiyze a peptide bond via a covalent acyl-enzyme intermediate, and aspartic, giutamic and metaiioproteases activate a water moiecuie to hydroiyze the peptide bond in a non-covalent manner.

Leupeptin serine, cysteine, threonine proteases competitive, transition state analog PI arginine specificity trypsin 130 nM cathepsin B- 6nM (51)... 

Another class of transition-state inhibitors is the peptide aldehyde inhibitors (Fig. 7). Aldehydes inhibit cysteine, serine, and threonine proteases via a covalent, reversible mechanism, and metaUoproteases using an analogous but nonco-valent mechanism. Aldehydes were discovered in screens for protease inhibitors from microorganisms and generally consist of a peptidyl moiety that binds in the non-prime specificity sites with a C-terminal aldehyde group. These inhibitors are... 

Figure 7 Various transition-state protease inhibitors. Bortezomib is an approved drug for the treatment of multiple myeloma. It is a boronic acid analog that inhibits the proteosome, a threonine protease. The boronic acid moiety can adopt a tetrahedral conformation in the active site. Pepstatin is a peptidyl aspartic acid inhibitor. The reactive statine group binds to the catalytic machinery, and the chiral hydroxyl group of the statine mimics the tetrahedral geometry of the transition state. Idinavir is an approved HIV 1 Protease inhibitor that binds to the active site via a hydroxyethylene transition state isostere. Aldehydes are also transition state analogs, which are susceptible to nucleophilic attack. In cysteine, serine and threonine proteases, this results in a covalent, reversible inhibition mechanism.

Another ATP-dependent protease identified among heat shock proteins of E. coli is known as HslV-HslU or (ClpQ-ClpY). It has a threonine protease active site and is even more closely remeniscient of eukaryotic proteasomes. Also active in E. coli is another ring-like protease, a membrane-bormd zinc endopeptidase FtsH (or HflB). " Similar eukaryotic proteases also exist. ... 

Epoxides, aziridines, -lactams as irreversible inhibitors of serine, cysteine, and threonine proteases 02CRV4639. 

Fig. 10.4 (continued) tide bond cleavage. In the cysteine (and also serine and threonine) proteases, the nucleophile is the protease type amino acid (in this case cysteine) which forms a covalent bond with the carbon atom of the bond to be cleaved (covalent catalysis) in contrast to the metalloprotei-nases and aspartic proteases which use an activated water molecule to attack the carbon atom to be cleaved (noncovalent catalysis). In covalent catalysis, a nearby histidine residue normally functions as a base to activate the mechanism, whereas in noncovalent catalysis, the protease type serves as an acid and base, with an ancillary histidine (aspartate proteases) or aspartate or glutamate residue acting as the nucleophile (Fig. 8.2b) (Modified from Fig. 9.18 in Berg., et al., Biochemistry, 5th Ed. 2002, W.H. Freeman Co., New York)...

Unlike other proteases, the proteasome utilizes threonine protease activity. The N-terminal threonines act as active nucleophiles that attack the amide carbonyl moiety of target proteins, cleave the amide bond to form an acyl-enzyme intermediate, and subsequently hydrolyze to release the free proteasome threonine residue and the remaining peptide residue. Small molecules, including natural product-based proteasome inhibitors have significantly contributed to our understanding of the specifics of proteasome protease function (reviewed by Tsukamoto and Yokosawa ). 

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