Active site cysteine

Zhang, Z.-Y., Dixon, J. E. Active site labeling of the yersinia protein tyrosine phosphatase The determination of the pKa of active site cysteine and the function of the conserved histidine 402. Biochem. 32 (1993) 9340-9345. 

Oxidation (e.g., PTPs inactivation via oxidation of the active site cystein)... 

Rhinoviri are the causal agents of common colds in humans. Viral replication and maturation is dependent on proteolytic processing of a viral polyprotein by a cysteine protease known as 3C protease. The active-site cysteine in 3C protease... 

The first disclosed natural product was cerulenin (15), an irreversible inhibitor of FabB. This hydrophobic epoxide locates itself in the hydro-phobic groove of the acyl site and reacts covalently with the active site cysteine [26]. However, 15 was also found to inhibit eukaryotic fatty acid synthase. 

Masamune, S., Palmer, M.A.J., Gamboni, R., Thompson, S., Davis, J.T., Williams, S.F., Peoples, O.P., Sinskey, A.J., and Walsh, C.T. (1989) Bio-Claisen condensation catalyzed by thiolase from Zoogloea ramigera. Active site cysteine residues. Chemtracts Org. Chem. 2, 247-251. 

The most convenient way of categorizing the classes of cathepsin inhibitors is based on the nature of the electrophilic warhead that interacts with the sulfhydryl group of the active site cysteine residue. Since a large portion of the binding energy of a cysteine protease inhibitor comes from the covalent interaction with this thiol, the properties of the resulting molecules are largely derived from the electrophile. In broad terms, these inhibitors can be broken down into ketone and nitrile-based reversible covalent inhibitors, or the more recent non-covalent inhibitors based on an aminoaniline template. 

The final class of inhibitor to be described contains no electrophilic warhead to interact with the sulfhydryl group of the active site cysteine. The binding affinity of these non-covalent, competitive inhibitors is partly achieved through lipophilic PI interactions of an aminoethylaniline moiety [68]. Electron-donating substituents on the aniline are required for potency against Cat K [7]. 

We have also developed targeted library approaches towards cysteine proteases, which are important pharmaceutical targets due to their role in the pathogenesis of many diseases.1251 A common feature of virtually all cysteine protease inhibitors is an electrophilic functionality, such as a carbonyl or a Michael acceptor, which can react with the nucleophilic active site cysteine residue. We specifi-... 

The mechanism by which A-esterases hydrolyze organophosphates is not completely understood. Involvement of a phosphorylated active-site cysteine and displacement of an activated H20 molecule are two possible hypotheses (see Sect. 3.7.1) [56], A-Esterases comprise enzymes that hydrolyze aryl esters, paraoxon (2.2) and related organophosphate pesticides, and diisopropyl-fluorophosphate (DFP, diisopropyl phosphorofluoridate, 2.3) and related compounds, including nerve gases. These enzymes are found in the current nomenclature listed under arylesterases, aryldialkylphosphatase, and diisop-ropyl-fluorophosphatase. 

After the formation of an acyl adenylate, the similarities between MoeB and El appear to come to an end (Figure 3.2B). In the El enzymes an active-site cysteine residue attacks the ubiquitin adenylate forming the El-ubiquitin thioester. E. coli MoeB contains nine cysteine residues, four of which are involved in coordinating the zinc atom. Sequence alignments show that among the remaining cysteines... 

Fig. 4.1. Fundamentals of the ubiquitin system. Adapted from Ref [5]. Figure 4.1 shows the fundamentals of the ubiquitin system. (1) Ubiquitin is synthesized in linear chains or as the N-terminal fusion with small ribosomal subunits that are cleaved by de-ubiquitylating enzymes to form the active protein. Ubiquitin is then activated in an ATP-dependent manner by El where a thiolester linkage is formed. It is then transthiolated to the active-site cysteine of an E2. E2s interact with E3s and with substrates and mediate either the indirect (in the case of HECT E3s) or direct transfer of ubiquitin to substrate. A number of factors can affect this process. We know that interactions with Hsp70 can facilitate ubiquitylation in specific instances and competition for lysines on substrates with the processes of acetylation and sumoylation may be inhibitory in certain instances. (2) For efficient proteasomal targeting to occur chains of ubiquitin linked internally through K48 must be formed. This appears to involve multiple...

Fig. 5.2. E2 sequence alignments. Sequences of the twelve E2s found in the PDB. The active-site cysteine is colored green, identical residues colored red, and conserved residues colored blue.

Fig. 5.3. Ubcl3 (IJBB). Canonical a/fS E2 fold with the active-site cysteine shown in ball-and-stick.

Fig. S.4. Ubcl/ubiquitin thiol ester complex model (1 FXT). The surface of Ubcl is shown with residues implicated in ubiquitin binding colored purple and the active-site cysteine colored yellow. Ubiquitin is colored green.

Fig. S.S. UbcH7/c-Cbl complex (IFBV).The surface of UbcH7 is shown with residues interacting with the c-Cbl RING domain shown in red and the active-site cysteine shown in yellow. c-Cbl is colored green.

The closest approach of a RING-domain residue to the active-site cysteine of UbcH7 is about 15 A, arguing against a role for RING E3s in chemical catalysis [106]. Instead, RING E3s have been proposed to facilitate ubiquitination by inducing physical proximity of the E2/ubiquitin thiol ester and the substrate [23, 30, 106, 109]. Catalysis would result from the increased local concentrations of the two reactants (discussed further below). 

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