Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The primary processing of the poliovirus polyprotein is catalyzed by 2A protease (2Apro) which cleaves at the 1D/2A junction in a very rapid cotranslational reaction. In addition, 2Apro also indirectly induces cleavage of the p220 component of eIF-4F, which results in selective inhibition of host protein synthesis. Earlier studies have indicated that 2Apro is related to 3C protease (3Cpro) and is structurally similar to trypsin-like serine proteases with the substitution of Cys109 as the nucleophile. We noticed that 2Apro of enteroviruses and rhinoviruses contains a specific motif of Cys55-Xaa-Cys57-Xaan-Cys115-Xaa-His117 which is absolutely conserved, but which is not found in viral 3Cpro or known cellular serine proteases. To better understand the specific roles these conserved cysteine and histidine residues played in the structure/function of 2Apro, we constructed a series of 2Apro mutants by site-specific mutagenesis and analyzed the mutant enzymes with respect to their biochemical properties. Conservative amino acid replacements at Cys55, Cys57, Cys115, or His117 resulted, in each case, in a complete loss of both in cis and in trans activities of 2Apro. To determine the function of these residues, we examined the biochemical/structural features of 2Apro expressed in a cell-free rabbit reticulocyte lysate system. Gel mobility shift and chemical modification data suggest that these cysteine residues do not form intra-molecular disulfide linkages as a structural feature of 2Apro. However, studies with metal chelators did not eliminate the possibility that 2Apro contains a metal-binding ligand. Finally, our results suggest that these conserved cysteine and histidine residues, including Cys55, Cys57, Cys115, and His117, are critical in maintaining the active conformation of 2Apro structure and essential in supporting the catalytic activity of 2Apro.
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PMID:Characterization of the roles of conserved cysteine and histidine residues in poliovirus 2A protease. 131 Jan 93

Proteolytic processing of poliovirus polyprotein is carried out by the products of two viral genes, 2A and 3C. 2A protease catalyzes cleavage of the polyprotein of type 1 poliovirus at two sites, one a cis cleavage at the 2A N-terminus and the other a trans cleavage within the 3D polymerase. In addition to polyprotein cleavage activity, 2A protease also indirectly induces cleavage of the p220 component of the cap-binding protein complex, which results in selective inhibition of host protein synthesis. Molecular genetic and biochemical analyses of 2A protease were performed to test its putative homology to small trypsin-like serine proteases and to examine the roles of individual amino acids in the reaction mechanism of 2A protease. A recombinant plasmid containing poliovirus 1C, 1D, and 2A gene sequences was expressed in a cell-free transcription/translation system, resulting in synthesis of a precursor protein that underwent efficient self-processing and produced mature 2A protease. To identify residues involved in the catalytic center and/or substrate-binding loops, we generated a series of 2A mutants by site-specific mutagenesis of this plasmid. Mutants were then expressed in vitro and tested for autocatalytic cis cleavage activity, trans cleavage of the 1D/2A junction, and trans-activation of p220-specific protease. Our data suggest that the conserved His20, Asp38, and Cys109 residues recently proposed to be equivalent to the catalytic triad of known serine proteases may comprise the catalytic triad of 2A protease. Surprisingly, Asp38 could be replaced with glutamic acid and retain autocatalytic function. Other amino acid substitutions at Tyr88, Tyr89, and Thr124 suggested that these residues lie in loops involved in substrate binding. Biochemical studies with protease inhibitors indicate that 2A protease activity is blocked by inhibitors specific for serine and cysteine proteases. Overall, the results are consistent with the hypothesis that 2A proteinase is structurally similar to the trypsin-like family of serine proteases with the substitution of cysteine 109 as the active site nucleophile.
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PMID:Identification of essential amino acid residues in the functional activity of poliovirus 2A protease. 185 Sep 21

The picornavirus family contains several human pathogens including human rhinovirus (HRV) and hepatitis A virus (HAV). In the case of HRVs, these small single-stranded positive-sense RNA viruses translate their genetic information into a polyprotein precursor which is further processed mainly by two viral proteases designated 2A and 3C. The 2A protease (2Apro) makes the first cleavage between the structural and non-structural proteins, while 3C protease (3Cpro) catalyzes most of the remaining internal cleavages. It has been shown that both 2Apro and 3Cpro are cysteine proteases but their overall protein folding is more like trypsin-type serine proteases. Due to their unique protein structure and essential roles in viral replication, 2Apro and 3Cpro have been viewed as excellent targets for antiviral intervention. In recent years, considerable efforts have been made in the development of antiviral compounds targeting these proteases. This article summarizes the recent approaches in the design of novel 2A and 3C protease inhibitors as potential antiviral agents for the treatment of picornaviral infections.
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PMID:Protease inhibitors as potential antiviral agents for the treatment of picornaviral infections. 1039 29

The picornavirus family contains several human pathogens including human rhinovirus (HRV) and hepatitis A virus (HAV). In the case of HRVs, these small single-stranded positive-sense RNA viruses translate their genetic information into a polyprotein precursor which is further processed mainly by two viral proteases designated 2A and 3C. The 2A protease (2Apro) makes the first cleavage between the structural and non-structural proteins, while 3C protease (3Cpro) catalyzes most of the remaining internal cleavages. It has been shown that both 2Apro and 3Cpro are cysteine proteases but their overall protein folding is more like trypsin-type serine proteases. Due to their unique protein structure and essential roles in viral replication, 2Apro and 3Cpro have been viewed as excellent targets for antiviral intervention. In recent years, considerable efforts have been made in the development of antiviral compounds targeting these proteases. This article summarizes the recent approaches in the design of novel 2A and 3C protease inhibitors as potential antiviral agents for the treatment of picornaviral infections.
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PMID:Protease inhibitors as potential antiviral agents for the treatment of picornaviral infections. 1154 9