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Zheng F, Yi W, Liu W, Zhu H, Gong P, Pan Z. A positively charged surface patch on the pestivirus NS3 protease module plays an important role in modulating NS3 helicase activity and virus production. Arch Virol 2021; 166:1633-1642. [PMID: 33787991 DOI: 10.1007/s00705-021-05055-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 02/08/2021] [Indexed: 10/21/2022]
Abstract
Pestivirus nonstructural protein 3 (NS3) is a multifunctional protein with protease and helicase activities that are essential for virus replication. In this study, we used a combination of biochemical and genetic approaches to investigate the relationship between a positively charged patch on the protease module and NS3 function. The surface patch is composed of four basic residues, R50, K74 and K94 in the NS3 protease domain and H24 in the structurally integrated cofactor NS4APCS. Single-residue or simultaneous four-residue substitutions in the patch to alanine or aspartic acid had little effect on ATPase activity. However, single substitutions of R50, K94 or H24 or a simultaneous four-residue substitution resulted in apparent changes in the helicase activity and RNA-binding ability of NS3. When these mutations were introduced into a classical swine fever virus (CSFV) cDNA clone, a single substitution at K94 or a simultaneous four-residue substitution (Qua_A or Qua_D) impaired the production of infectious virus. Furthermore, the replication efficiency of the CSFV variants was partially correlated with the helicase activity of NS3 in vitro. Our results suggest that the conserved positively charged patch on NS3 plays an important role in modulating the NS3 helicase activity in vitro and CSFV production.
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Affiliation(s)
- Fengwei Zheng
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Weicheng Yi
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Weichi Liu
- Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, China
| | - Hongchang Zhu
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Peng Gong
- Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, China.
| | - Zishu Pan
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China.
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Shady NH, Khattab AR, Ahmed S, Liu M, Quinn RJ, Fouad MA, Kamel MS, Muhsinah AB, Krischke M, Mueller MJ, Abdelmohsen UR. Hepatitis C Virus NS3 Protease and Helicase Inhibitors from Red Sea Sponge ( Amphimedon) Species in Green Synthesized Silver Nanoparticles Assisted by in Silico Modeling and Metabolic Profiling. Int J Nanomedicine 2020; 15:3377-3389. [PMID: 32494136 PMCID: PMC7231760 DOI: 10.2147/ijn.s233766] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 01/29/2020] [Indexed: 12/14/2022] Open
Abstract
Background Hepatitis C virus (HCV) infection is a major cause of hepatic diseases all over the world. This necessitates the need to discover novel anti-HCV drugs to overcome emerging drug resistance and liver complications. Purpose Total extract and petroleum ether fraction of the marine sponge (Amphimedon spp.) were used for silver nanoparticle (SNP) synthesis to explore their HCV NS3 helicase- and protease-inhibitory potential. Methods Characterization of the prepared SNPs was carried out with ultraviolet-visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The metabolomic profile of different Amphimedon fractions was assessed using liquid chromatography coupled with high-resolution mass spectrometry. Fourteen known compounds were isolated and their HCV helicase and protease activities assessed using in silico modeling of their interaction with both HCV protease and helicase enzymes to reveal their anti-HCV mechanism of action. In vitro anti-HCV activity against HCV NS3 helicase and protease was then conducted to validate the computation results and compared to that of the SNPs. Results Transmission electron–microscopy analysis of NPs prepared from Amphimedon total extract and petroleum ether revealed particle sizes of 8.22–14.30 nm and 8.22–9.97 nm, and absorption bands at λmax of 450 and 415 nm, respectively. Metabolomic profiling revealed the richness of Amphimedon spp. with different phytochemical classes. Bioassay-guided isolation resulted in the isolation of 14 known compounds with anti-HCV activity, initially revealed by docking studies. In vitro anti–HCV NS3 helicase and protease assays of both isolated compounds and NPs further confirmed the computational results. Conclusion Our findings indicate that Amphimedon, total extract, petroleum ether fraction, and derived NPs are promising biosources for providing anti-HCV drug candidates, with nakinadine B and 3,4-dihydro-6-hydroxymanzamine A the most potent anti-HCV agents, possessing good oral bioavailability and penetration power.
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Affiliation(s)
- Nourhan Hisham Shady
- Department of Pharmacognosy, Faculty of Pharmacy, Deraya University, Universities Zone, Minia 61111, Egypt
| | - Amira R Khattab
- Department of Pharmacognosy, College of Pharmacy, Arab Academy for Science, Technology and Maritime Transport, Alexandria 1029, Egypt
| | - Safwat Ahmed
- Department of Pharmacognosy, Faculty of Pharmacy, Suez Canal University, Ismailia, Egypt 41522
| | - Miaomiao Liu
- Griffith Institute for Drug Discovery, Griffith University, Brisbane, Queensland 4111, Australia
| | - Ronald J Quinn
- Griffith Institute for Drug Discovery, Griffith University, Brisbane, Queensland 4111, Australia
| | - Mostafa A Fouad
- Department of Pharmacognosy, Faculty of Pharmacy, Minia University, Minia 61519, Egypt
| | - Mohamed Salah Kamel
- Department of Pharmacognosy, Faculty of Pharmacy, Minia University, Minia 61519, Egypt
| | - Abdullatif Bin Muhsinah
- Department of Pharmacognosy, College of Pharmacy, King Khalid University, Abha 61441, Saudi Arabia
| | - Markus Krischke
- Department of Pharmaceutical Biology, Julius-von-Sachs Institute for Biological Sciences, University of Würzburg, Würzburg 97082, Germany
| | - Martin J Mueller
- Department of Pharmaceutical Biology, Julius-von-Sachs Institute for Biological Sciences, University of Würzburg, Würzburg 97082, Germany
| | - Usama Ramadan Abdelmohsen
- Department of Pharmacognosy, Faculty of Pharmacy, Deraya University, Universities Zone, Minia 61111, Egypt.,Department of Pharmacognosy, Faculty of Pharmacy, Minia University, Minia 61519, Egypt
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Biochemical Characterization of Middle East Respiratory Syndrome Coronavirus Helicase. mSphere 2016; 1:mSphere00235-16. [PMID: 27631026 PMCID: PMC5014916 DOI: 10.1128/msphere.00235-16] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 08/19/2016] [Indexed: 11/20/2022] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) helicase is a superfamily 1 helicase containing seven conserved motifs. We have cloned, expressed, and purified a Strep-fused recombinant MERS-CoV nonstructural protein 13 (M-nsp13) helicase. Characterization of its biochemical properties showed that it unwound DNA and RNA similarly to severe acute respiratory syndrome CoV nsp13 (S-nsp13) helicase. We showed that M-nsp13 unwound in a 5'-to-3' direction and efficiently unwound the partially duplex RNA substrates with a long loading strand relative to those of the RNA substrates with a short or no loading strand. Moreover, the Km of ATP for M-nsp13 is inversely proportional to the length of the 5' loading strand of the partially duplex RNA substrates. Finally, we also showed that the rate of unwinding (ku) of M-nsp13 is directly proportional to the length of the 5' loading strand of the partially duplex RNA substrate. These results provide insights that enhance our understanding of the biochemical properties of M-nsp13. IMPORTANCE Coronaviruses are known to cause a wide range of diseases in humans and animals. Middle East respiratory syndrome coronavirus (MERS-CoV) is a novel coronavirus discovered in 2012 and is responsible for acute respiratory syndrome in humans in the Middle East, Europe, North Africa, and the United States of America. Helicases are motor proteins that catalyze the processive separation of double-stranded nucleic acids into two single-stranded nucleic acids by utilizing the energy derived from ATP hydrolysis. MERS-CoV helicase is one of the most important viral replication enzymes of this coronavirus. Herein, we report the first bacterial expression, enzyme purification, and biochemical characterization of MERS-CoV helicase. The knowledge obtained from this study might be used to identify an inhibitor of MERS-CoV replication, and the helicase might be used as a therapeutic target.
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Protease Inhibitors Block Multiple Functions of the NS3/4A Protease-Helicase during the Hepatitis C Virus Life Cycle. J Virol 2015; 89:5362-70. [PMID: 25740995 DOI: 10.1128/jvi.03188-14] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 02/23/2015] [Indexed: 01/11/2023] Open
Abstract
UNLABELLED Hepatitis C virus (HCV) NS3 is a multifunctional protein composed of a protease domain and a helicase domain linked by a flexible linker. Protease activity is required to generate viral nonstructural (NS) proteins involved in RNA replication. Helicase activity is required for RNA replication, and genetic evidence implicates the helicase domain in virus assembly. Binding of protease inhibitors (PIs) to the protease active site blocks NS3-dependent polyprotein processing but might impact other steps of the virus life cycle. Kinetic analyses of antiviral suppression of cell culture-infectious genotype 1a strain H77S.3 were performed using assays that measure different readouts of the viral life cycle. In addition to the active-site PI telaprevir, we examined an allosteric protease-helicase inhibitor (APHI) that binds a site in the interdomain interface. By measuring nucleotide incorporation into HCV genomes, we found that telaprevir inhibits RNA synthesis as early as 12 h at high but clinically relevant concentrations. Immunoblot analyses showed that NS5B abundance was not reduced until after 12 h, suggesting that telaprevir exerts a direct effect on RNA synthesis. In contrast, the APHI could partially inhibit RNA synthesis, suggesting that the allosteric site is not always available during RNA synthesis. The APHI and active-site PI were both able to block virus assembly soon (<12 h) after drug treatment, suggesting that they rapidly engage with and block a pool of NS3 involved in assembly. In conclusion, PIs and APHIs can block NS3 functions in RNA synthesis and virus assembly, in addition to inhibiting polyprotein processing. IMPORTANCE The NS3/4A protease of hepatitis C virus (HCV) is an important antiviral target. Currently, three PIs have been approved for therapy of chronic hepatitis C, and several others are in development. NS3-dependent cleavage of the HCV polyprotein is required to generate the mature nonstructural proteins that form the viral replicase. Inhibition of protease activity can block RNA replication by preventing expression of mature replicase components. Like many viral proteins, NS3 is multifunctional, but how PIs affect stages of the HCV life cycle beyond polyprotein processing has not been well studied. Using cell-based assays, we show here that PIs can directly inhibit viral RNA synthesis and also block a late stage in virus assembly/maturation at clinically relevant concentrations.
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Comparison of structural architecture of HCV NS3 genotype 1 versus Pakistani genotype 3a. BIOMED RESEARCH INTERNATIONAL 2014; 2014:749254. [PMID: 25401105 PMCID: PMC4221965 DOI: 10.1155/2014/749254] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Revised: 08/10/2014] [Accepted: 08/19/2014] [Indexed: 11/17/2022]
Abstract
This study described the structural characterization of Pakistani HCV NS3 GT3a in parallel with genotypes 1a and 1b NS3. We investigated the role of amino acids and their interaction patterns in different HCV genotypes by crystallographic modeling. Different softwares were used to study the interaction pattern, for example, CLCBIO sequence viewer, MODELLER, NMRCLUST, ERRAT score, and MODELLER. Sixty models were produced and clustered into groups and the best model of PK-NCVI/Pk3a NS3 was selected and studied further to check the variability with other HCV NS3 genotypes. This study will help in future to understand the structural architecture of HCV genome variability and to further define the conserved targets for antiviral agents.
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Junaid M, Angsuthanasombat C, Wikberg JES, Ali N, Katzenmeier G. Modulation of enzymatic activity of dengue virus nonstructural protein NS3 nucleoside triphosphatase/helicase by poly(U). BIOCHEMISTRY (MOSCOW) 2014; 78:925-32. [PMID: 24228882 DOI: 10.1134/s0006297913080105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The nonstructural protein 3 (NS3) appears to be the most promising target for anti-flavivirus therapy because of its multiple enzymatic activities that are indispensable for virus replication. NS3 of dengue virus type 2 (DEN2) is composed of two domains, a serine protease in the N-terminal domain (NS3pro) and RNA-stimulated nucleoside triphosphatase (NTPase)/RNA helicase at the C-terminus (NS3h). NS3 plays an important role in viral replication and the coordinated regulation of all the catalytic activities in the full-length NS3 protein. In this study, a plasmid harboring the NS3 helicase domain (NS3h) was constructed by PCR. The 56.5 kDa NS3h protein was purified by metal-chelate affinity chromatography followed by renaturation, mediated by artificial chaperone-assisted refolding, which yielded the active helicase. NTPase activity was assayed with Malachite Green. The NTPase activity in the presence of poly(U) showed a higher turnover number (kcat) and a lower Km value than without poly(U). The activity increased approximately fourfold in the presence of polynucleotides. This indicates that NTPase activity of dengue NS3 can be stimulated by polynucleotides. A helicase assay based on internal fluorescence quenching was conducted using short internally quenched DNA oligonucleotides as substrates. Significant fluorescence signaling increase was observed in the absence of polynucleotides such as poly(U). No unwinding activity was observed with addition of poly(U). The approach we describe here is useful for the further characterization of substrate specificity and for the design of high-throughput assays aimed at discovery of inhibitors against NS3 NTPase/helicase activities.
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Affiliation(s)
- M Junaid
- Laboratory of Molecular and Cellular Microbiology, Institute of Molecular Biosciences, Mahidol University, Salaya, 73170, Thailand.
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7
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Hepatitis C virus and vaccine development. INTERNATIONAL JOURNAL OF MOLECULAR AND CELLULAR MEDICINE 2014; 3:207-15. [PMID: 25635247 PMCID: PMC4293608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 08/02/2014] [Accepted: 09/10/2014] [Indexed: 12/05/2022]
Abstract
The prevalence of Hepatitis C virus (HCV) is approximately 3% around the world. This virus causes chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. The effectiveness of interferon-α and ribavirin therapy is about 50% and is associated with significant toxicity and cost. Hence, generating new vaccines or drugs is an obligation. However, there is no vaccine available for clinical use. DNA vaccines have some advantages such as producing feasibility and generating intensive cellular and humoral immune responses. Activation and improvement of natural immune defense mechanisms is a necessity for the development of an effective HCV vaccine. This article discusses the current status of therapies for hepatitis C, the promising new therapies and the experimental strategies to develop an HCV vaccine.
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Grammatikos G, Jabara CB, Ahmad MQ, Herrmann E, Zeuzem S, Welsch C. Genetic background for development of resistance mutations within the HCV NS3 protease-helicase in direct acting antiviral naive patients. Antivir Ther 2013; 19:455-61. [PMID: 24457994 DOI: 10.3851/imp2734] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/08/2013] [Indexed: 10/25/2022]
Abstract
BACKGROUND Subtype-specific response to ketoamide NS3 protease inhibitors is observed in patients with genotype 1 HCV infection. Whether the genetic diversity in the molecular target site of ketoamide compounds prior to treatment plays a role for resistance development and lower treatment response in subtype 1a is poorly understood. METHODS Using a public database, we retrieved worldwide NS3-sequence information of 581 dominant HCV variants from patients chronically infected with genotype 1 that were naive to direct-acting antivirals. We applied measures from phylogeny to study the pretreatment genetic diversity and complexity in NS3 full-length as well as the protease-helicase interface for subtype 1a and 1b, respectively. RESULTS We found polymorphic sites more frequently in variants of subtype 1b than subtype 1a. Moreover, a significantly higher number of synonymous and non-synonymous substitutions were found in subtype 1b (P<0.001). Transitions were more frequent than transversions, most notably in subtype 1a, whereas the higher average number of nucleotide differences per site was found in subtype 1b. A comparison of NS3 full-length versus domain interface residues for both subtypes revealed a significant difference only for synonymous substitutions (P<0.001). CONCLUSIONS Our study suggests that the nature of a mismatch nucleotide exchange in NS3 may constitute an important viral genetic factor for response to ketoamide protease inhibitors. Our analysis further suggests that the subtype-specific pace of resistance development seen in clinical trials is not primarily related to differences in genetic diversity in the direct acting antiviral naive population, but rather appears to correlate with the natural frequency of transition mutations characteristic of each subtype.
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Affiliation(s)
- Georgios Grammatikos
- Department of Internal Medicine I, Frankfurt University Hospital, Goethe University, Frankfurt am Main, Germany
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Saalau-Bethell SM, Woodhead AJ, Chessari G, Carr MG, Coyle J, Graham B, Hiscock SD, Murray CW, Pathuri P, Rich SJ, Richardson CJ, Williams PA, Jhoti H. Discovery of an allosteric mechanism for the regulation of HCV NS3 protein function. Nat Chem Biol 2012; 8:920-5. [PMID: 23023261 PMCID: PMC3480716 DOI: 10.1038/nchembio.1081] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 08/23/2012] [Indexed: 01/23/2023]
Abstract
Here we report a highly conserved new binding site located at the interface between the protease and helicase domains of the hepatitis C virus (HCV) NS3 protein. Using a chemical lead, identified by fragment screening and structure-guided design, we demonstrate that this site has a regulatory function on the protease activity via an allosteric mechanism. We propose that compounds binding at this allosteric site inhibit the function of the NS3 protein by stabilizing an inactive conformation and thus represent a new class of direct-acting antiviral agents.
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10
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Development of chemical inhibitors of the SARS coronavirus: viral helicase as a potential target. Biochem Pharmacol 2012; 84:1351-8. [PMID: 22935448 PMCID: PMC7092843 DOI: 10.1016/j.bcp.2012.08.012] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 08/14/2012] [Accepted: 08/15/2012] [Indexed: 11/21/2022]
Abstract
Severe acute respiratory syndrome (SARS) was the first pandemic in the 21st century to claim more than 700 lives worldwide. However, effective anti-SARS vaccines or medications are currently unavailable despite being desperately needed to adequately prepare for a possible SARS outbreak. SARS is caused by a novel coronavirus, and one of its components, a viral helicase, is emerging as a promising target for the development of chemical SARS inhibitors. In the following review, we describe the characterization, family classification, and kinetic movement mechanisms of the SARS coronavirus (SCV) helicase—nsP13. We also discuss the recent progress in the identification of novel chemical inhibitors of nsP13 in the context of our recent discovery of the strong inhibition of the SARS helicase by natural flavonoids, myricetin and scutellarein. These compounds will serve as important resources for the future development of anti-SARS medications.
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Wen G, Xue J, Shen Y, Zhang C, Pan Z. Characterization of classical swine fever virus (CSFV) nonstructural protein 3 (NS3) helicase activity and its modulation by CSFV RNA-dependent RNA polymerase. Virus Res 2009; 141:63-70. [PMID: 19185595 DOI: 10.1016/j.virusres.2008.12.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 12/19/2008] [Accepted: 12/23/2008] [Indexed: 10/21/2022]
Abstract
Classical swine fever virus (CSFV) nonstructural protein 3 (NS3) is believed to possess three enzyme activities that are likely to be essential for virus replication: a serine protease located in the N-terminus and NTPase as well as helicase activities located in the C-terminus. In this report, we expressed NS3 helicase domain (NS3h) in E. coli and characterized its helicase activity. The NS3h helicase activity was dependent on the presence of NTP and divalent cations, with a preference for ATP and Mn(2+), and required the substrates possessing a 3' un-base-paired region on the RNA template strand. The NS3h helicase activity was proportional to increasing lengths of the 3' un-base-paired regions up to 16 nucleotides of the RNA substrates. We also investigated the modulation of NS3 NTPase/helicase activities by NS3 protease domain and NS5B, an RNA-dependent RNA polymerase (RdRp). Our data showed that the NS3 protease domain enhanced the helicase activity of NS3 but had no effect on its NTPase activity. For the truncated NS3 (helicase domain, NS3h), both NTPase and helicase activities were up-regulated by NS5B. However, for the full-length NS3 (NS3FL), the NTPase activity, but not the helicase activity, was stimulated by NS5B. Maltose-binding protein (MBP) pull-down as well as enzyme-linked immunosorbent assays confirmed the specific interaction between NS3 and NS5B.
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Affiliation(s)
- Guoyuan Wen
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China
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Bermúdez-Aguirre AD, Padilla-Noriega L, Zenteno E, Reyes-Leyva J. Identification of Amino Acid Variants in the Hepatitis C Virus Non-Structural Protein 4A. TOHOKU J EXP MED 2009; 218:165-75. [DOI: 10.1620/tjem.218.165] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Alejandro Daniel Bermúdez-Aguirre
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México
- Laboratorio de Virología, Centro de Investigaciones Biomédicas de Oriente, Instituto Mexicano del Seguro Social, Hospital General de Zona No. 5
| | - Luis Padilla-Noriega
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México
| | - Edgar Zenteno
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México
- Facultad de Medicina Humana, Universidad Ricardo Palma
| | - Julio Reyes-Leyva
- Laboratorio de Virología, Centro de Investigaciones Biomédicas de Oriente, Instituto Mexicano del Seguro Social, Hospital General de Zona No. 5
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NS3 helicase domains involved in infectious intracellular hepatitis C virus particle assembly. J Virol 2008; 82:7624-39. [PMID: 18508894 DOI: 10.1128/jvi.00724-08] [Citation(s) in RCA: 172] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
A mutation within subdomain 1 of the hepatitis C virus (HCV) NS3 helicase (NS3-Q221L) (M. Yi, Y. Ma, J. Yates, and S. M. Lemon, J. Virol. 81:629-638, 2007) rescues a defect in production of infectious virus by an intergenotypic chimeric RNA (HJ3). Although NS3-Gln-221 is highly conserved across HCV genotypes, the Leu-221 substitution had no effect on RNA replication or NS3-associated enzymatic activities. However, while transfection of unmodified HJ3 RNA failed to produce either extracellular or intracellular infectious virus, transfection of HJ3 RNA containing the Q221L substitution (HJ3/QL) resulted in rapid accumulation of intracellular infectious particles with release into extracellular fluids. In the absence of the Q221L mutation, both NS5A and NS3 were recruited to core protein on the surface of lipid droplets, but there was no assembly of core into high-density, rapidly sedimenting particles. Further analysis demonstrated that a Q221N mutation minimally rescued virus production and led to a second-site I399V mutation in subdomain 2 of the helicase. Similarly, I399V alone allowed only low-level virus production and led to selection of an I286V mutation in subdomain 1 of the helicase which fully restored virus production, confirming the involvement of both major helicase subdomains in the assembly process. Thus, multiple mutations in the helicase rescue a defect in an early-intermediate step in virus assembly that follows the recruitment of NS5A to lipid droplets and precedes the formation of dense intracellular viral particles. These data reveal a previously unsuspected role for the NS3 helicase in early virion morphogenesis and provide a new perspective on HCV assembly.
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Wen G, Chen C, Luo X, Wang Y, Zhang C, Pan Z. Identification and characterization of the NTPase activity of classical swine fever virus (CSFV) nonstructural protein 3 (NS3) expressed in bacteria. Arch Virol 2007; 152:1565-73. [PMID: 17447110 DOI: 10.1007/s00705-007-0969-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Accepted: 03/09/2007] [Indexed: 11/26/2022]
Abstract
The nonstructural protein 3 (NS3) of members of the family Flaviviridae possesses multiple enzyme activities that are likely to be essential for viral replication. Here, we cloned and expressed full-length CSFV NS3 protein (NS3FL) and its N-terminal truncated version (ntNS3) in E. coli. NTPase activities of the purified NS3FL and ntNS3 proteins and their reaction conditions were investigated. The results showed that CSFV NS3FL and ntNS3 proteins contained a specific polynucleotide-stimulated NTPase acitivity. Characterization of ntNS3 NTPase activity showed that optimal reaction conditions with respect to pH, MgCl2 and monovalent cations were similar to those of bovine viral diarrhea virus (BVDV) and hepatitis C virus (HCV). Site-directed mutagenesis analysis demonstrated that the GxGK(232)T to GxGAT mutation in the conserved motif I abolished the NTPase activity of ntNS3, whereas substitution of TATPA(354) for TATPV in the motif III had no effect on the enzyme activity. Moreover, the kinetic properties (K(m) and k(cat)) of CSFV NS3 were more similar to those of BVDV. Our results provide insight into the structure-function relationship of CSFV NS3 and facilitate our understanding of its role in the replication cycle of CSFV.
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Affiliation(s)
- G Wen
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China
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Umareddy I, Chao A, Sampath A, Gu F, Vasudevan SG. Dengue virus NS4B interacts with NS3 and dissociates it from single-stranded RNA. J Gen Virol 2006; 87:2605-2614. [PMID: 16894199 DOI: 10.1099/vir.0.81844-0] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Dengue virus, a member of the family Flaviviridae of positive-strand RNA viruses, has seven non-structural proteins: NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5. Except for enzymic activities contained within NS3 and NS5, the roles of the other proteins in virus replication and pathogenesis are not well defined. In this study, a physical interaction between NS4B and the helicase domain of NS3 was identified by using a yeast two-hybrid assay. This interaction was further confirmed by biochemical pull-down and immunoprecipitation assays, both with purified proteins and with dengue virus-infected cell lysates. NS4B co-localized with NS3 in the perinuclear region of infected human cells. Furthermore, NS4B dissociated NS3 from single-stranded RNA and consequently enhanced the helicase activity of NS3 in an in vitro unwinding assay. These results suggest that NS4B modulates dengue virus replication via its interaction with NS3.
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Affiliation(s)
- Indira Umareddy
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos Building, Singapore 138670
| | - Alex Chao
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos Building, Singapore 138670
| | - Aruna Sampath
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos Building, Singapore 138670
| | - Feng Gu
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos Building, Singapore 138670
| | - Subhash G Vasudevan
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos Building, Singapore 138670
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Rosales-León L, Ortega-Lule G, Ruiz-Ordaz B. Analysis of the domain interactions between the protease and helicase of NS3 in dengue and hepatitis C virus. J Mol Graph Model 2006; 25:585-94. [PMID: 16762573 DOI: 10.1016/j.jmgm.2006.04.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2005] [Revised: 04/01/2006] [Accepted: 04/01/2006] [Indexed: 01/28/2023]
Abstract
Flaviviridae non-structural 3 protein (NS3) is a multifunctional enzyme, composed by a protease domain (NS3pro) and an RNA helicase domain (NS3hel). The activities present in NS3 have proved to be critical for viral replication. The replicative cycle of Flaviviridae requires coordinated regulation of all the activities present in the full-length NS3 protein, however, the exact nature of these interactions remains unclear. The present work aimed to determine common structural features between NS3 of dengue and hepatitis C viruses and to characterize residues involved in the regulation of the interdomain motions between NS3pro and NS3hel. Analysis of the root mean square (RMS) variation shows that NS3pro increases the stability of subdomain 1 of the RNA helicase. Moreover, the dynamic behaviour of the carboxy terminus of NS3hel, supports the hypothesis that, upon release of the carboxy-terminus from NS3pro, the residues involved in this interaction are folded back into the last alpha-helix. Using normal mode analysis, we characterized slow collective motions of NS3, and observed that the two lowest-frequency normal modes are enough to describe reorientations of NS3pro relative to NS3hel. These movements induced an increment in the exposure of the active site of NS3pro that can be important during the proteolytic processing of the viral polyprotein. The third low-frequency normal mode was correlated to subdomain reorientations of NS3hel, similar to those proposed during NTP hydrolysis and dsRNA unwinding. Based on these data, we support a dynamic model, in which the domain movements between NS3pro and NS3hel result in the regulation of its activities.
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Affiliation(s)
- L Rosales-León
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, Apartado Postal 70228, 04510 México, D.F., México
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17
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Samuilova O, Krogerus C, Fabrichniy I, Hyypiä T. ATP hydrolysis and AMP kinase activities of nonstructural protein 2C of human parechovirus 1. J Virol 2006; 80:1053-8. [PMID: 16379008 PMCID: PMC1346857 DOI: 10.1128/jvi.80.2.1053-1058.2006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The highly conserved picornavirus 2C proteins, thought to be involved in genome replication, contain three motifs found in NTPases/helicases of superfamily III. We report that human parechovirus 1 2C displays Mg2+-dependent ATP diphosphohydrolase activity in vitro, whereas other nucleoside triphosphates are not substrates for the hydrolysis. We also found that the 2C protein has an enzymatic activity that converts AMP to a corresponding diphosphate using ADP or ATP as a phosphate donor. In addition, we observed that ATP hydrolysis results in 2C autophosphorylation. These findings indicate that the parechovirus 2C protein has enzymatic activities, which may contribute to several functions in the viral replication cycle.
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Affiliation(s)
- Olga Samuilova
- Haartman Institute, Department of Virology, P.O. Box 21, FIN-00014 University of Helsinki, Helsinki, Finland.
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18
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Abstract
To date, although many viral infections can be successfully prevented via vaccination, we lack effective knowledge of vaccines for numerous important human pathogens, including hepatitis C virus (HCV) and human immunodeficiency virus (HIV). Accordingly, antiviral drugs will be needed to treat many viral diseases. Virally encoded enzymes and cellular enzymes adapted for use by viruses for replication might represent useful targets for antiviral drugs. Drugs that target either a viral or cellular polypeptide hold different implications. Inhibitors of unique viral functions have a lower risk of toxicity, whereas inhibitors of cellular enzymes that are used by viruses have a narrower window for efficacy without creating toxicity. All viruses seem to require a helicase function for replication. HCV encodes a viral RNA helicase, and recent findings have shown that HIV-1 adapts a cellular RNA helicase for its viral lifecycle. These observations raise the possibility of small-molecule helicase inhibitors as a general mode of antiviral therapy. Helicases fall into three super-families (SF1, SF2 and SF3) with conserved motifs. The conserved motifs are associated with conserved helicase function. However, outside of the conserved motifs the primary sequences and tertiary structures between helicases are differ greatly. In this regard, differences in primary sequence and tertiary structure between the helicase of a viral pathogen and that of cellular helicases can be exploited to confer specificity to an antiviral inhibitor. The conformation of an active helicase can be broadly divided into an 'open' and a 'closed' complex. Strategies for identifying small-molecule helicase inhibitors include: inhibiting NTPase activity by direct competition with NTP binding; competitively inhibit nucleic-acid binding; inhibiting NTP hydrolysis or NDP release by blocking the movement of domain 2; inhibiting the process that couples NTP hydrolysis to translocation and unwinding of nucleic acid; inhibiting unwinding by sterically blocking helicase translocation; and inhibiting unwinding. Other potential inhibitory mechanisms include those that change the physical conformation of the helicase, or those that disrupt helicase turnover, or those that inhibit helicase interaction with other crucial proteins. Preclinical proof of concept for helicase inhibitors as antiviral agents has been obtained for HSV. This breakthrough finding provides the best evidence to date that it is possible to develop selective, potent inhibitors of a viral helicase as antiviral agents. Searches are ongoing for antihelicase molecules that have activity against HCV or HIV-1.
Although there has been considerable progress in the development of antiviral agents in recent years, there is still a pressing need for new drugs both to improve on the properties of existing agents and to combat the problem of viral resistance. Helicases, both viral and human, have recently emerged as novel targets for the treatment of viral infections. Here, we discuss the role of these enzymes, factors affecting their potential as drug targets and progress in the development of agents that inhibit their activity using the hepatitis C virus-encoded helicase NS3 and the cellular helicase DDX3 adopted for use by HIV-1 as examples.
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Affiliation(s)
- Ann D. Kwong
- Vertex Pharmaceuticals Inc., 130 Waverly Street, Cambridge, 02139 Massachusetts USA
| | - B. Govinda Rao
- Vertex Pharmaceuticals Inc., 130 Waverly Street, Cambridge, 02139 Massachusetts USA
| | - Kuan-Teh Jeang
- The National Institute of Allergy and Infectious Diseases, 9000 Rockville Pike, Bethesda, 20892 Maryland USA
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19
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Lee S, Lee JH, Kee YH, Park MY, Myung H. Partial reconstitution of hepatitis C virus RNA polymerization by heterologous expression of NS5B polymerase and template RNA in bacterial cell. Virus Res 2005; 114:158-63. [PMID: 16099067 DOI: 10.1016/j.virusres.2005.06.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2005] [Revised: 06/13/2005] [Accepted: 06/13/2005] [Indexed: 11/29/2022]
Abstract
The hepatitis C virus (HCV) is a major etiological agent causing chronic hepatitis in humans. Since the virus does not grow in a cell culture, the direct measurement of viral replication is impossible. Therefore, the current study presents a surrogate model system using a viral polymerase and RNA template. A plasmid expressing the HCV NS5B polymerase was maintained with a plasmid containing a reporter gene in an Escherichia coli cell. The reporter construct contained the HCV 5' untranslated region (UTR) followed by a luciferase gene with a specific orientation so that a minus-sense transcript containing the luciferase fused to the 5' UTR was produced after the initial transcription. When the HCV NS5B polymerase was expressed in the same cell, the primary transcript was recognized by the polymerase due to the presence of the minus-sense 5' UTR, and a secondary transcript containing a plus-sense luciferase gene was produced. Thus, a simple luciferase assay was able to measure the HCV NS5B polymerase activity. The production of minus- and plus-sense transcripts was confirmed by an RT-PCR, while the production of HCV NS5B and expression of the reporter luciferase in the bacterial cell were confirmed by immunofluorescence microscopy. The polymerization occurred in the absence of any other viral/host factors. Accordingly, this would appear to be the first study to demonstrate that the heterologous expression of an animal viral RNA polymerase and its template in a bacterial cell can partially reconstitute the polymerization reaction.
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Affiliation(s)
- Sangyoon Lee
- Department of Bioscience and Biotechnology, Hankuk University of Foreign Studies, Yong-In, Kyung-Gi Do 449-791, Republic of Korea
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20
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Zhang C, Cai Z, Kim YC, Kumar R, Yuan F, Shi PY, Kao C, Luo G. Stimulation of hepatitis C virus (HCV) nonstructural protein 3 (NS3) helicase activity by the NS3 protease domain and by HCV RNA-dependent RNA polymerase. J Virol 2005; 79:8687-97. [PMID: 15994762 PMCID: PMC1168731 DOI: 10.1128/jvi.79.14.8687-8697.2005] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2005] [Accepted: 03/22/2005] [Indexed: 01/28/2023] Open
Abstract
Hepatitis C virus (HCV) nonstructural protein 3 (NS3) possesses multiple enzyme activities. The N-terminal one-third of NS3 primarily functions as a serine protease, while the remaining two-thirds of NS3 serve as a helicase and nucleoside triphosphatase. Whether the multiple enzyme activities of NS3 are functionally interdependent and/or modulated by other viral NS proteins remains unclear. We performed biochemical studies to examine the functional interdependence of the NS3 protease and helicase domains and the modulation of NS3 helicase by NS5B, an RNA-dependent RNA polymerase (RdRp). We found that the NS3 protease domain of the full-length NS3 (NS3FL) enhances the NS3 helicase activity. Additionally, HCV RdRp stimulates the NS3FL helicase activity by more than sevenfold. However, the helicase activity of the NS3 helicase domain was unaffected by HCV RdRp. Glutathione S-transferase pull-down as well as fluorescence anisotropy results revealed that the NS3 protease domain is required for specific NS3 and NS5B interaction. These findings suggest that HCV RdRp regulates the functions of NS3 during HCV replication. In contrast, NS3FL does not increase NS5B RdRp activity in vitro, which is contrary to a previously published report that the HCV NS3 enhances NS5B RdRp activity.
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Affiliation(s)
- Chen Zhang
- Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY 40536, USA
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21
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Bartenschlager R, Frese M, Pietschmann T. Novel insights into hepatitis C virus replication and persistence. Adv Virus Res 2005; 63:71-180. [PMID: 15530561 DOI: 10.1016/s0065-3527(04)63002-8] [Citation(s) in RCA: 227] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Hepatitis C virus (HCV) is a small enveloped RNA virus that belongs to the family Flaviviridae. A hallmark of HCV is its high propensity to establish a persistent infection that in many cases leads to chronic liver disease. Molecular studies of the virus became possible with the first successful cloning of its genome in 1989. Since then, the genomic organization has been delineated, and viral proteins have been studied in some detail. In 1999, an efficient cell culture system became available that recapitulates the intracellular part of the HCV life cycle, thereby allowing detailed molecular studies of various aspects of viral RNA replication and persistence. This chapter attempts to summarize the current state of knowledge in these most actively worked on fields of HCV research.
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Affiliation(s)
- Ralf Bartenschlager
- Department of Molecular Virology, University of Heidelberg, Im Neuenheimer Feld 345, 69120 Heidelberg, Germany
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22
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Kyono K, Miyashiro M, Taguchi I. Expression and purification of a hepatitis C virus NS3/4A complex, and characterization of its helicase activity with the Scintillation Proximity Assay system. J Biochem 2004; 135:245-52. [PMID: 15047727 DOI: 10.1093/jb/mvh029] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The C-terminal two-thirds of nonstructural protein 3 (NS3) of hepatitis C virus (HCV) possesses RNA helicase activity. This enzyme is considered to be involved in viral replication, and is expected to be one of the target molecules of anti-HCV drugs. Previously, we established a high-throughput screening system for HCV helicase inhibitors using the Scintillation Proximity Assay (SPA) system [Kyono, K. et al. (1998) ANAL: BIOCHEM: 257, 120-126]. Here, we show improvement of the preparation method for the HCV NS3/4A complex. Alteration of the expression region led to an increase in protein expression. The partially purified full-length NS3 protein showed higher NS3 protease activity without the cofactor NS4A peptide than the truncated protease domain with the cofactor peptide, suggesting that this protein formed a complex with NS4A. NS3 further purified to homogeneity, as judged on silver staining, remained in a complex with NS4A. Characterization of the helicase activity of this full NS3/4A complex using the SPA helicase assay system revealed that this enzyme preferred Mn(2+), and that the optimal pH was 6.0-6.5. The NS3/4A complex could act on a DNA template but could not unwind the M13DNA/DNA substrate.
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Affiliation(s)
- Kiyoshi Kyono
- Medicinal Chemistry Research Laboratories, Tanabe Seiyaku Co., Ltd., 16-89 Kashima 3-chome, Yodogawa-ku, Osaka 532-8505.
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23
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Lam AMI, Rypma RS, Frick DN. Enhanced nucleic acid binding to ATP-bound hepatitis C virus NS3 helicase at low pH activates RNA unwinding. Nucleic Acids Res 2004; 32:4060-70. [PMID: 15289579 PMCID: PMC506820 DOI: 10.1093/nar/gkh743] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The molecular basis of the low-pH activation of the helicase encoded by the hepatitis C virus (HCV) was examined using either a full-length NS3 protein/NS4A cofactor complex or truncated NS3 proteins lacking the protease domain, which were isolated from three different viral genotypes. All proteins unwound RNA and DNA best at pH 6.5, which demonstrate that conserved NS3 helicase domain amino acids are responsible for low-pH enzyme activation. DNA unwinding was less sensitive to pH changes than RNA unwinding. Both the turnover rate of ATP hydrolysis and the K(m) of ATP were similar between pH 6 and 10, but the concentration of nucleic acid needed to stimulate ATP hydrolysis decreased almost 50-fold when the pH was lowered from 7.5 to 6.5. In direct-binding experiments, HCV helicase bound DNA weakly at high pH only in the presence of the non-hydrolyzable ATP analog, ADP(BeF3). These data suggest that a low-pH environment might be required for efficient HCV RNA translation or replication, and support a model in which an acidic residue rotates toward the RNA backbone upon ATP binding repelling nucleic acid from the binding cleft.
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Affiliation(s)
- Angela M I Lam
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595, USA
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24
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Ivanov KA, Thiel V, Dobbe JC, van der Meer Y, Snijder EJ, Ziebuhr J. Multiple enzymatic activities associated with severe acute respiratory syndrome coronavirus helicase. J Virol 2004; 78:5619-32. [PMID: 15140959 PMCID: PMC415832 DOI: 10.1128/jvi.78.11.5619-5632.2004] [Citation(s) in RCA: 333] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Severe acute respiratory syndrome coronavirus (SARS-CoV), a newly identified group 2 coronavirus, is the causative agent of severe acute respiratory syndrome, a life-threatening form of pneumonia in humans. Coronavirus replication and transcription are highly specialized processes of cytoplasmic RNA synthesis that localize to virus-induced membrane structures and were recently proposed to involve a complex enzymatic machinery that, besides RNA-dependent RNA polymerase, helicase, and protease activities, also involves a series of RNA-processing enzymes that are not found in most other RNA virus families. Here, we characterized the enzymatic activities of a recombinant form of the SARS-CoV helicase (nonstructural protein [nsp] 13), a superfamily 1 helicase with an N-terminal zinc-binding domain. We report that nsp13 has both RNA and DNA duplex-unwinding activities. SARS-CoV nsp13 unwinds its substrates in a 5'-to-3' direction and features a remarkable processivity, allowing efficient strand separation of extended regions of double-stranded RNA and DNA. Characterization of the nsp13-associated (deoxy)nucleoside triphosphatase ([dNTPase) activities revealed that all natural nucleotides and deoxynucleotides are substrates of nsp13, with ATP, dATP, and GTP being hydrolyzed slightly more efficiently than other nucleotides. Furthermore, we established an RNA 5'-triphosphatase activity for the SARS-CoV nsp13 helicase which may be involved in the formation of the 5' cap structure of viral RNAs. The data suggest that the (d)NTPase and RNA 5'-triphosphatase activities of nsp13 have a common active site. Finally, we established that, in SARS-CoV-infected Vero E6 cells, nsp13 localizes to membranes that appear to be derived from the endoplasmic reticulum and are the likely site of SARS-CoV RNA synthesis.
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Affiliation(s)
- Konstantin A Ivanov
- Institute of Virology and Immunology, University of Würzburg, Würzburg, Germany
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25
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Tsantrizos YS. The design of a potent inhibitor of the hepatitis C virus NS3 protease:BILN 2061?From the NMR tube to the clinic. Biopolymers 2004; 76:309-23. [PMID: 15386268 DOI: 10.1002/bip.20127] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The virally encoded serine protease NS3/NS4A is essential to the life cycle of the hepatitis C virus (HCV), an important human pathogen causing chronic hepatitis, cirrhosis of the liver, and hepatocellular carcinoma. Until very recently, the design of inhibitors for the HCV NS3 protease was limited to large peptidomimetic compounds with poor pharmacokinetic properties, making drug discovery an extremely challenging endeavor. In our quest for the discovery of a small-molecule lead that could block replication of the hepatitis C virus by binding to the HCV NS3 protease, the critical protein-polypeptide interactions between the virally encoded NS3 serine protease and its polyprotein substrate were investigated. Lead optimization of a substrate-based hexapeptide, guided by structural data, led to the understanding of the molecular dynamics and electronic effects that modulate the affinity of peptidomimetic ligands for the active site of this enzyme. Macrocyclic beta-strand scaffolds were designed that allowed the discovery of potent, highly selective, and orally bioavailable compounds. These molecules were the first HCV NS3 protease inhibitors reported that inhibit replication of HCV subgenomic RNA in a cell-based replicon assay at low nanomolar concentrations. Optimization of their biopharmaceutical properties led to the discovery of the clinical candidate BILN 2061. Oral administration of BILN 2061 to patients infected with the hepatitis C genotype 1 virus resulted in an impressive reduction of viral RNA levels, establishing proof-of-concept for HCV NS3 protease inhibitors as therapeutic agents in humans.
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Affiliation(s)
- Youla S Tsantrizos
- Boehringer Ingelheim (Canada) Ltd., Research and Development, 2100 Cunard Street, Laval (Québec) H7S 2G5, Canada.
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26
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Isaguliants MG, Petrakova NV, Mokhonov VV, Pokrovskaya K, Suzdaltzeva YG, Krivonos AV, Zaberezhny AD, Garaev MM, Smirnov VD, Nordenfelt E. DNA immunization efficiently targets conserved functional domains of protease and ATPase/helicase of nonstructural 3 protein (NS3) of human hepatitis C virus. Immunol Lett 2003; 88:1-13. [PMID: 12853154 DOI: 10.1016/s0165-2478(03)00051-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Nonstructural protein 3 (NS3) of human hepatitis C virus (HCV) is a conserved multi-functional protein essential for replication and translation of viral RNA and polyprotein processing. Early T-cell response against NS3 is capable of restricting viremia. We aimed at characterizing the immunogenicity in gene immunization of the conserved regions of NS3 critical for protein folding and activity. C57BL/6 mice were injected with NS3 gene of Russian HCV 1b isolate 274933RU. Immunization did not exert any overt histological changes and had no long-term effects on the immune status of NS3 gene-recipients. The immune response in NS3 gene-recipients was screened by antibody ELISA, T-cell proliferation test and immune assays for specific cytokine production. T-lymphocytes of NS3 gene-recipients proliferated in response to peptides representing conserved regions of protease and ATPase/helicase. Stimulated T-lymphocytes produced IL-2, and in response to protease-derived peptides, also IFN-gamma. Potent and long-lasting antibody response was raised against conserved NS3 regions including "Greek-key" motif of protease, motifs II, V and polynucleotide-binding domains of ATPase/helicase. Thus, gene immunization effectively targeted conserved regions critical for NS3 protease and helicase function. In type and specificity, immune response of NS3 gene-immunized mice mimicked immunity achieved in the acute self-limiting HCV infection of human and primates and in virus-exposed healthy individuals, indicating promiscuity of NS3 as immunogen.
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Affiliation(s)
- Maria G Isaguliants
- D.I. Ivanovsky Institute of Virology, Gamaleja str. 16, 123098, Moscow, Russia.
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27
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Lam AMI, Keeney D, Eckert PQ, Frick DN. Hepatitis C virus NS3 ATPases/helicases from different genotypes exhibit variations in enzymatic properties. J Virol 2003; 77:3950-61. [PMID: 12634355 PMCID: PMC150621 DOI: 10.1128/jvi.77.7.3950-3961.2003] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The NS3 ATPase/helicase was isolated and characterized from three different infectious clones of hepatitis C virus (HCV). One helicase was from a genotype that normally responds to therapy (Hel-2a), and the other two were from more resistant genotypes, 1a (Hel-1a) and 1b (Hel-1b). Although the differences among these helicases are generally minor, all three enzymes have distinct properties. Hel-1a is less selective for nucleoside triphosphates, Hel-1b hydrolyzes nucleoside triphosphates less rapidly, and Hel-2a unwinds DNA more rapidly and binds DNA more tightly than the other two enzymes. Unlike related proteins, different nucleic acid sequences stimulate ATP hydrolysis by HCV helicase at different maximum rates and with different apparent efficiencies. This nucleic acid stimulation profile is conserved among the enzymes, but it does not result entirely from differential DNA-binding affinities. Although the amino acid sequences of the three proteins differ by up to 15%, one variant amino acid that is critical for helicase action was identified. NS3 residue 450 is a threonine in Hel-1a and Hel-1b and is an isoleucine in Hel-2a. A mutant Hel-1a with an isoleucine substituted for threonine 450 unwinds DNA more rapidly and binds DNA more tightly than the parent protein.
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Affiliation(s)
- Angela M I Lam
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595, USA
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28
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Hardy RW, Marcotrigiano J, Blight KJ, Majors JE, Rice CM. Hepatitis C virus RNA synthesis in a cell-free system isolated from replicon-containing hepatoma cells. J Virol 2003; 77:2029-37. [PMID: 12525637 PMCID: PMC140877 DOI: 10.1128/jvi.77.3.2029-2037.2003] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A number of hepatitis C virus (HCV) proteins, including NS5B, the RNA-dependent RNA polymerase, were detected in membrane fractions from Huh7 cells containing autonomously replicating HCV RNA replicons. These membrane fractions were used in a cell-free system for the analysis of HCV RNA replication. Initial characterization revealed a reaction in which the production of replicon RNA increased over time at temperatures ranging from 25 to 40 degrees C. Heparin sensitivity and nucleotide starvation experiments suggested that de novo initiation was occurring in this system. Both Mn2+ and Mg2+ cations could be used in the reaction; however, concentrations of Mn2+ greater than 1 mM were inhibitory. Compounds shown to inhibit recombinant NS3 and NS5B activity in vitro were found to inhibit RNA synthesis in the cell-free system. This system should be useful for biochemical analysis of HCV RNA synthesis by a multisubunit membrane-associated replicase and for evaluating potential antiviral agents identified in biochemical or cell-based screens.
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Affiliation(s)
- Richard W Hardy
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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29
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Minczuk M, Piwowarski J, Papworth MA, Awiszus K, Schalinski S, Dziembowski A, Dmochowska A, Bartnik E, Tokatlidis K, Stepien PP, Borowski P. Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA. Nucleic Acids Res 2002; 30:5074-86. [PMID: 12466530 PMCID: PMC137961 DOI: 10.1093/nar/gkf647] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and sub-fractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a K(m) of 41.9 micro M and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution.
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Affiliation(s)
- Michal Minczuk
- Department of Genetics, University of Warsaw, Pawinskiego 5A, 02-106 Warsaw, Poland
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30
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Borowski P, Schalinski S, Schmitz H. Nucleotide triphosphatase/helicase of hepatitis C virus as a target for antiviral therapy. Antiviral Res 2002; 55:397-412. [PMID: 12206878 DOI: 10.1016/s0166-3542(02)00096-7] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The RNA nucleoside triphosphatase (NTPase)/helicases represent a large family of proteins that are detected in almost all biological systems where RNA plays a central role. The enzymes are capable of enzymatically unwinding duplex RNA structures by disrupting the hydrogen bonds that keep the two strands together. The strand separating activity is associated with hydrolysis of nucleoside triphosphate (NTP). Because of this, potential specific inhibitors of NTPase/helicases could act by one or more of the following mechanisms: (i) inhibition of NTPase activity by interference with NTP binding, (ii) inhibition of NTPase activity by an allosteric mechanism and (iii) inhibition of the coupling of NTP hydrolysis at the unwinding reaction. There are also other inhibitory mechanisms conceivable, which may involve a modulation of the interaction of the enzyme with its RNA substrate, for example, (iv) the competitive inhibition of RNA binding and (v) the inhibition of the unwinding by sterical blockade of the translocation of the NTPase/helicase along the polynucleotide chain. NTPase/helicase has also been identified in the viral genome of hepatitis C virus (HCV) which is a member of the Flaviviridae family. It is conceivable that the inhibition of the unwinding activity of the enzyme leads to the inhibition of virus replication and this may represent a novel antiviral strategy. This review updates the current spectrum of inhibitors targeting different mechanisms by which the NTPase and/or helicase activities of the HCV NTPase/helicase are inhibited. Consequently, some of the compounds might be important as antiviral agents against HCV.
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Affiliation(s)
- Peter Borowski
- Abteilung für Virologie, Bernhard-Nocht-Institut für Tropenmedizin, 20359 Hamburg, Germany.
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31
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Abstract
The ability of a helicase to bind single-stranded nucleic acid is critical for nucleic acid unwinding. The helicase from the hepatitis C virus, NS3 protein, binds to the 3'-DNA or the RNA strand during unwinding. As a step to understand the mechanism of unwinding, DNA binding properties of the helicase domain of NS3 (NS3h) were investigated by fluorimetric binding equilibrium titrations. The global analysis of the binding data by a combinatorial approach was done using MATLAB. NS3h interactions with single-stranded DNA (ssDNA) are 300-1000-fold tighter relative to duplex DNA. The NS3h protein binds to ssDNA less than 15 nt in length with a stoichiometry of one protein per DNA. The minimal ssDNA binding site of NS3h helicase was determined to be 8 nucleotides with the microscopic K(d) of 2-4 nm or an observed free energy of -50 kJ/mol. These NS3h-DNA interactions are highly sensitive to salt, and the K(d) increases 4 times when the NaCl concentration is doubled. Multiple HCV helicase proteins bind to ssDNA >15 nucleotides in length, with an apparent occluded site of 8-11 nucleotides. The DNA binding data indicate that the interactions of multiple NS3h protein molecules with long ssDNA are both noncooperative and sequence-independent. We discuss the DNA binding properties of HCV helicase in relation to other superfamily 1 and 2 helicases. These studies provide the basis to investigate the DNA binding interactions with the unwinding substrate and their modulation by the ATPase activity of HCV helicase.
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Affiliation(s)
- Mikhail K Levin
- Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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32
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Poliakov A, Hubatsch I, Shuman CF, Stenberg G, Danielson UH. Expression and purification of recombinant full-length NS3 protease-helicase from a new variant of Hepatitis C virus. Protein Expr Purif 2002; 25:363-71. [PMID: 12182815 DOI: 10.1016/s1046-5928(02)00042-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Viral mRNA extracted from the serum of a patient infected with HCV strain 1a was used for cloning, expression, and purification of full-length Hepatitis C NS3 protein. Sequencing of the protease gene identified the virus to be a new variant closely related to strain H77, differing in 15 out of 631 amino acids in the NS3 protein, none of which were predicted to be directly involved in catalysis, binding of substrate, or cofactor. A pBAD expression system was used to express the enzyme with an N-terminal tag in Escherichia coli. Purification from the soluble cellular fraction was achieved by Ni(2+)-IMAC and PolyU Sepharose affinity chromatography. The dependence of the proteolytic activity of the full-length NS3 protein on ionic strength, glycerol concentration, and a peptide corresponding to the activating region of NS4A was analyzed and used to design an activity assay that is suitable for inhibition studies. The kinetic constants (k(cat) and K(M)) for catalysis and the inhibitory potencies (IC(50) and K(i)) of five product-based hexapeptide inhibitors were comparable to those reported for the truncated NS3 protein. Detailed kinetic and inhibition studies using this variant of full-length NS3 can increase the understanding of the enzymatic characteristics of NS3, reveal the importance of the substituted amino acids and the significance of the genetic variability for design of effective inhibitors of the virus, and is thus of relevance for drug discovery.
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Affiliation(s)
- Anton Poliakov
- Department of Biochemistry, Uppsala University, BMC, Box 576, SE-751 23 Uppsala, Sweden
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33
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Pang PS, Jankowsky E, Planet PJ, Pyle AM. The hepatitis C viral NS3 protein is a processive DNA helicase with cofactor enhanced RNA unwinding. EMBO J 2002; 21:1168-76. [PMID: 11867545 PMCID: PMC125889 DOI: 10.1093/emboj/21.5.1168] [Citation(s) in RCA: 180] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2001] [Revised: 12/03/2001] [Accepted: 01/09/2002] [Indexed: 01/22/2023] Open
Abstract
The RNA helicase/protease NS3 plays a central role in the RNA replication of hepatitis C virus (HCV), a cytoplasmic RNA virus that represents a major worldwide health problem. NS3 is, therefore, an important drug target in the effort to combat HCV. Most work has focused on the protease, rather than the helicase, activities of the enzyme. In order to further characterize NS3 helicase activity, we evaluated individual stages of duplex unwinding by NS3 alone and in complex with cofactor NS4A. Despite a putative replicative role in RNA unwinding, we found that NS3 alone is a surprisingly poor helicase on RNA, but that RNA activity is promoted by cofactor NS4A. In contrast, NS3 alone is a highly processive helicase on DNA. Phylogenetic analysis suggests that this robust DNA helicase activity is not vestigial and may have specifically evolved in HCV. Given that HCV has no replicative DNA intermediate, these findings suggest that NS3 may have the capacity to affect host DNA.
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Affiliation(s)
- Phillip S. Pang
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, Medical Scientist Training Program, Columbia College of Physicians and Surgeons, New York, NY, Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH, Integrated Program in Cellular, Molecular and Biophysical Sciences and Howard Hughes Medical Institute, Columbia University, New York, NY, USA Corresponding author e-mail:
| | - Eckhard Jankowsky
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, Medical Scientist Training Program, Columbia College of Physicians and Surgeons, New York, NY, Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH, Integrated Program in Cellular, Molecular and Biophysical Sciences and Howard Hughes Medical Institute, Columbia University, New York, NY, USA Corresponding author e-mail:
| | - Paul J. Planet
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, Medical Scientist Training Program, Columbia College of Physicians and Surgeons, New York, NY, Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH, Integrated Program in Cellular, Molecular and Biophysical Sciences and Howard Hughes Medical Institute, Columbia University, New York, NY, USA Corresponding author e-mail:
| | - Anna Marie Pyle
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, Medical Scientist Training Program, Columbia College of Physicians and Surgeons, New York, NY, Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH, Integrated Program in Cellular, Molecular and Biophysical Sciences and Howard Hughes Medical Institute, Columbia University, New York, NY, USA Corresponding author e-mail:
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Abstract
The Hepatitis C virus is a positive-stranded RNA virus which is the causal agent for a chronic liver infection afflicting more than 170,000,000 people world-wide. The HCV genome is approximately 9.6 kb in length and the proteome encoded is a polyprotein of a little more than 3000 amino acid residues. This polyprotein is processed by a combination of host and viral proteases into structural and non-structural proteins. The functions of most of these proteins have been established by analogy to other viruses and by sequence homology to known proteins, as well as subsequent biochemical analysis. Two of the non-structural proteins, NS4b and NS5a, are still of unknown function. The development of antivirals for this infectious agent has been hampered by the lack of robust and economical cell culture and animal infection systems. Recent progress in the molecular virology of HCV has come about due to the definition of molecular clones, which are infectious in the chimpanzee, the development of a subgenomic replicon system in Huh7 cells, and the description of a transgenic mouse model for HCV infection. Recent progress in the structural biology of the virus has led to the determination of high resolution three-dimensional structures of a number of the key virally encoded enzymes, including the NS3 protease, NS3 helicase, and NS5b RNA-dependent RNA polymerase. In some cases these structures have been determined in complex with substrates, co-factors (NS4a), and inhibitors. Finally, a variety of techniques have been used to define host factors, which may be required for HCV replication, although this work is just beginning.
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Affiliation(s)
- S Rosenberg
- Department of Chemistry, University of California, Berkeley, CA 94720, USA.
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Abstract
Escherichia coli DbpA is a member of the DEAD/H family of proteins which has been shown to have robust ATPase activity only in the presence of a specific region of 23S rRNA. A series of bimolecular RNA substrates were designed based on this activating region of rRNA and used to demonstrate that DbpA is also a non-processive, sequence-specific RNA helicase. The high affinity of DbpA for the RNA substrates allowed both single and multiple turnover helicase assays to be performed. Helicase activity of DbpA is dependent on the presence of ATP or dATP, the sequence of the loop of hairpin 92 of 23S rRNA and the position of the substrate helix with respect to hairpin 92. This work indicates that certain RNA helicases require particular RNA structures in order for optimal unwinding activity to be observed.
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Affiliation(s)
| | - Olke C. Uhlenbeck
- Department of Chemistry and Biochemistry, 215 UCB, University of Colorado, Boulder, CO 80309-0215, USA
Corresponding author e-mail:
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36
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Rho J, Choi S, Seong YR, Choi J, Im DS. The arginine-1493 residue in QRRGRTGR1493G motif IV of the hepatitis C virus NS3 helicase domain is essential for NS3 protein methylation by the protein arginine methyltransferase 1. J Virol 2001; 75:8031-44. [PMID: 11483748 PMCID: PMC115047 DOI: 10.1128/jvi.75.17.8031-8044.2001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The NS3 protein of hepatitis C virus (HCV) contains protease and RNA helicase activities, both of which are likely to be essential for HCV propagation. An arginine residue present in the arginine-glycine (RG)-rich region of many RNA-binding proteins is posttranslationally methylated by protein arginine methyltransferases (PRMTs). Amino acid sequence analysis revealed that the NS3 protein contains seven RG motifs, including two potential RG motifs in the 1486-QRRGRTGRG-1494 motif IV of the RNA helicase domain, in which arginines are potentially methylated by PRMTs. Indeed, we found that the full-length NS3 protein is arginine methylated in vivo. The full-length NS3 protein and the NS3 RNA helicase domain were methylated by a crude human cell extract. The purified PRMT1 methylated the full-length NS3 and the RNA helicase domain, but not the NS3 protease domain. The NS3 helicase bound specifically and comigrated with PRMT1 in vitro. Mutational analyses indicate that the Arg(1493) in the QRR(1488)GRTGR(1493)G region of the NS3 RNA helicase is essential for NS3 protein methylation and that Arg(1488) is likely methylated. NS3 protein methylation by the PRMT1 was decreased in the presence of homoribopolymers, suggesting that the arginine-rich motif IV is involved in RNA binding. The results suggest that an arginine residue(s) in QRXGRXGR motif IV conserved in the virus-encoded RNA helicases can be posttranslationally methylated by the PRMT1.
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Affiliation(s)
- J Rho
- Cell Biology Laboratory, Korea Research Institute of Bioscience and Biotechnology, Yusong, Taejeon 305-333, Republic of Korea
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37
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Hicham Alaoui-Ismaili M, Gervais C, Brunette S, Gouin G, Hamel M, Rando RF, Bedard J. A novel high throughput screening assay for HCV NS3 helicase activity. Antiviral Res 2000; 46:181-93. [PMID: 10867156 DOI: 10.1016/s0166-3542(00)00085-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A novel assay for measurement of Hepatitis C virus (HCV) NS3 helicase activity was developed using Flashplate technology. This assay involves the use of a DNA duplex substrate and recombinant HCV NS3 produced in Escherichia coli. The DNA duplex consisted of a pair of oligonucleotides, one biotinylated, the other radiolabeled at their respective 5' termini. This DNA duplex was immobilized, via the biotin molecule, on the surface of a neutravidin-coated SMP103 Flashplate (NEN Life Science Products). Helicase activity results in the release of the radiolabeled oligonucleotide, which translates in signal reduction with respect to control wells. Biochemical characterization of the HCV NS3 helicase activity was performed using this assay. We demonstrated that the NS3-mediated unwinding is proportional to both the amount of DNA substrate in the well, and to the NS3 concentration in the reaction. Most of the NS3-mediated unwinding was achieved in the initial 60 min of incubation. As expected the reactions were ATP-dependent and found to be affected by the concentration of MgCl(2), MnCl(2), KCl, EDTA, and by pH. We found this assay to be highly reproducible since only slight variation was observed when a total of 68 helicase reactions were performed on one plate. Therefore, this Flashplate helicase assay is fast, convenient and reproducible. These criteria make it suitable for high throughput screening of potential NS3 helicase inhibitors.
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38
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Abstract
Lack of efficacy and significant side effects have severely limited the use of interferon-alpha (IFN-alpha) as the standard therapy for non-A non-B hepatitis (NANBH) caused by hepatitis C virus (HCV) and alternative, improved therapies are urgently sought. Attempts have been made to improve the potency and tolerability of IFN-alpha by adjusting dosing regimens, methods of delivery and length of treatment. Furthermore, a number of different agents have been used in combination wit IFN-alpha and, from these studies, therapeutic options have been galvanized by the synergistic effects of IFN-alpha and ribavirin. Nevertheless, the majority of patients with HCV still do not sustain lasting therapeutic benefit from this combination and continuing research is required to identify new therapeutic candidates that will have more potent antiviral activity and less severe side effects. This review focuses on the progress that has been made in this area and the prospects for new effective therapies in the near future.
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Affiliation(s)
- B E Clarke
- Virology Research Unit, GlaxoWellcome Medicine Research Centre, Stevenage, Hertfordshire, UK
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39
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Yang SH, Lee CG, Song MK, Sung YC. Internal cleavage of hepatitis C virus NS3 protein is dependent on the activity of NS34A protease. Virology 2000; 268:132-40. [PMID: 10683335 DOI: 10.1006/viro.1999.0168] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The nonstructural protein NS3 of the hepatitis C virus (HCV) is indispensable for virus replication and a multifunctional enzyme that contains three catalytic activities such as serine protease, helicase, and NTPase. Here, we demonstrated that the internal cleavage of the HCV NS3 protein occurs in various mammalian cells such as HepG2, COS-7, and NIH3T3. As is observed for the internal cleavage mechanism of the NS3 protein of dengue virus 2, the internal processing of HCV NS3 protein was catalyzed by the active NS3 serine protease and NS4A, but not NS3 alone. From the data acquired from extensive site-directed mutagenesis, we observed that the NS3 protein was internally cleaved at two different sites, FCH(1395) ||S(1396)KK and IPT(1428) ||S(1429)GD, within RNA helicase domain. The internal cleavage of NS3 protein by NS34A protease was also confirmed in a different isolate of HCV-1b strain. In addition, in vitro transforming assays demonstrated that the internal cleavage product of NS3, NS3a-1, appeared to have higher oncogenic potential than does intact NS3. Taken together, our results suggest that the internal cleavage of NS3 may be associated with the replication and oncogenesis of HCV.
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Affiliation(s)
- S H Yang
- Department of Life Science, Pohang University of Science and Technology, Pohang, Kyungbuk, Republic of Korea
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40
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Abstract
Hepatitis C Virus helicase activity has been mapped to the COOH-terminal 450 residues of the NS3 protein. Due to its complexity and presumed essentiality for viral replication, the helicase is an attractive target for drug discovery. The elucidation of the atomic structure of the HCV NS3 helicase in complex with oligonucleotide and with ADP has helped clarify our understanding of potential sites for inhibitor binding. Molecular details of the mechanism of this enzyme, and in particular, a better understanding of the mechanism by which ATP hydrolysis is coupled to unwinding of double-stranded substrate may facilitate more efficient structure-based drug design.
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Affiliation(s)
- A D Kwong
- Vertex Pharmaceuticals, Inc., Cambridge, MA 02139, USA
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41
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Reed KE, Rice CM. Overview of hepatitis C virus genome structure, polyprotein processing, and protein properties. Curr Top Microbiol Immunol 1999; 242:55-84. [PMID: 10592656 DOI: 10.1007/978-3-642-59605-6_4] [Citation(s) in RCA: 239] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- K E Reed
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110-1093, USA
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42
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Petrik J, Parker H, Alexander GJM. Human hepatic glyceraldehyde-3-phosphate dehydrogenase binds to the poly(U) tract of the 3' non-coding region of hepatitis C virus genomic RNA. J Gen Virol 1999; 80 ( Pt 12):3109-3113. [PMID: 10567641 DOI: 10.1099/0022-1317-80-12-3109] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The unique poly(U/UC) tract, the middle part of the tripartite 3' non-coding region (3'NCR) of hepatitis C virus (HCV) genomic RNA, may represent a recognition signal for the HCV replicase complex. In this study, several proteins binding specifically to immobilized ribooligonucleotide r(U)(25) mimicking this structure were identified using cytosolic extracts from HCV-negative or -positive liver explants, and a prominent 36 kDa protein was studied further. Competition experiments including homoribopolymers revealed binding affinities in the order: oligo/poly(U)>(A)>(C)>(G). The protein was identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a multifunctional protein known to bind RNA. GAPDH bound efficiently to the full-length HCV RNA and binding to various 3'NCR constructs revealed critical dependence upon the presence of the middle part of the 3'NCR. Polypyrimidine tract-binding protein, described previously to bind the 3'NCR, did not bind efficiently to the middle part of 3'NCR and was captured from liver extracts in considerably smaller quantities.
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Affiliation(s)
- Juraj Petrik
- Departments of Haematology1 and Medicine2, University of Cambridge, School of Clinical Medicine, Cambridge, UK
| | - Hayley Parker
- Departments of Haematology1 and Medicine2, University of Cambridge, School of Clinical Medicine, Cambridge, UK
| | - Graeme J M Alexander
- Departments of Haematology1 and Medicine2, University of Cambridge, School of Clinical Medicine, Cambridge, UK
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43
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Abstract
Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. HCV is a positive-strand genotype RNA virus with extensive genetic heterogeneity; HCV isolates define 6 major genotypes, and HCV circulates within an infected individual as a number of closely related but distinct species, termed a quasispecies. This article reviews characteristic aspects of HCV molecular biology and their implications for treatment and vaccine development.
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Affiliation(s)
- X Forns
- Hepatitis Viruses Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
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44
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Grassmann CW, Isken O, Behrens SE. Assignment of the multifunctional NS3 protein of bovine viral diarrhea virus during RNA replication: an in vivo and in vitro study. J Virol 1999; 73:9196-205. [PMID: 10516027 PMCID: PMC112953 DOI: 10.1128/jvi.73.11.9196-9205.1999] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Studies on the replication of the pestivirus bovine viral diarrhea virus (BVDV) were considerably facilitated by the recent discovery of an autonomous subgenomic BVDV RNA replicon (DI9c). DI9c comprises mainly the untranslated regions of the viral genome and the coding region of the nonstructural proteins NS3, NS4A, NS4B, NS5A, and NS5B. To assess the significance of the NS3-associated nucleoside triphosphatase/helicase activity during RNA replication and to explore other functional features of NS3, we generated a repertoire of DI9c derivatives bearing in-frame mutations in different parts of the NS3 coding unit. Most alterations resulted in deficient replicons, several of which encoded an NS3 protein with an inhibited protease function. Three lesions permitted replication, though at a lower level than that of the wild-type RNA, i.e., replacement of the third position of the DEYH helicase motif II by either T or F and an insertion of four amino acid residues in the C-terminal part of NS3. While polyprotein proteolysis was found to be almost unaffected in these latter replicons, in vitro studies with the purified mutant NS3 proteins revealed a significantly impaired helicase activity for the motif II substitutions. NS3 with a DEFH motif, moreover, showed a significantly lower ATPase activity. In contrast, the C-terminal insertion had no negative impact on the ATPase/RNA helicase activity of NS3. All three mutations affected the synthesis of both replication products-negative-strand intermediate and progeny positive-strand RNA-in a symmetric manner. Unexpectedly, various attempts to rescue or enhance the replication capability of nonfunctional or less functional DI9c NS3 derivatives, respectively, by providing intact NS3 in trans failed. Our experimental data thus demonstrate that the diverse enzymatic activities of the NS3 protein-in particular the ATPase/RNA helicase-play a pivotal role even during early steps of the viral replication pathway. They may further indicate the C-terminal part of NS3 to be an important functional determinant of the RNA replication process.
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Affiliation(s)
- C W Grassmann
- Institut für Virologie (FB Veterinärmedizin), Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany
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45
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Abstract
The NS3 protein of hepatitis C virus (HCV) is a bifunctional protein containing a serine protease in the N-terminal one-third, which is stimulated upon binding of the NS4A cofactor, and an RNA helicase in the C-terminal two-thirds. In this study, a C-terminal hexahistidine-tagged helicase domain of the HCV NS3 protein was expressed in Escherichia coli and purified to homogeneity by conventional chromatography. The purified HCV helicase domain has a basal ATPase activity, a polynucleotide-stimulated ATPase activity, and a nucleic acid unwinding activity and binds efficiently to single-stranded polynucleotide. Detailed characterization of the purified HCV helicase domain with regard to all four activities is presented. Recently, we published an X-ray crystallographic structure of a binary complex of the HCV helicase with a (dU)(8) oligonucleotide, in which several conserved residues of the HCV helicase were shown to be involved in interactions between the HCV helicase and oligonucleotide. Here, site-directed mutagenesis was used to elucidate the roles of these residues in helicase function. Four individual mutations, Thr to Ala at position 269, Thr to Ala at position 411, Trp to Leu at position 501, and Trp to Ala at position 501, produced a severe reduction of RNA binding and completely abolished unwinding activity and stimulation of ATPase activity by poly(U), although the basal ATPase activity (activity in the absence of polynucleotide) of these mutants remained intact. Alanine substitution at Ser-231 or Ser-370 resulted in enzymes that were indistinguishable from wild-type HCV helicase with regard to all four activities. A mutant bearing Phe at Trp-501 showed wild-type levels of basal ATPase, unwinding activity, and single-stranded RNA binding activity. Interestingly, ATPase activity of this mutant became less responsive to stimulation by poly(U) but not to stimulation by other polynucleotides, such as poly(C). Given the conservation of some of these residues in other DNA and RNA helicases, their role in the mechanism of unwinding of double-stranded nucleic acid is discussed.
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Affiliation(s)
- C Lin
- Vertex Pharmaceuticals Incorporated, Cambridge, Massachusetts 02139, USA.
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46
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Min KH, Sung YC, Choi SY, Ahn BY. Functional interactions between conserved motifs of the hepatitis C virus RNA helicase protein NS3. Virus Genes 1999; 19:33-43. [PMID: 10499448 DOI: 10.1023/a:1008184522153] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The hepatitis C virus NS3 gene encodes a RNA helicase with several sequence motifs conserved among the members of the DExH box protein family. The contributions of the sequence motifs to enzyme activity were assessed in this study by substitution of alanine for the Lys in the ATP binding motif GxGK (referred to as K1236A mutation), or for the Asp in the DExH motif (D1316A), or for the Arg in the middle of the QRxGRxGR motif known for RNA binding (R1490A). Histidine-tagged recombinant proteins of Mr 54,000 were expressed in Escherichia coli and purified by chromatography on nickel agarose. All three mutants were severely defective in ATPase and RNA helicase activities, but loss of the ATPase activity was not dependent on polynucleotide cofactors. With the exception of R1490A mutant, a stable complex was formed between dsRNA substrates and recombinant proteins, indicating that the arginine-rich motif is required for efficient RNA binding. Complex formation was not affected by omission of ATP or substitution by a non-hydrolyzable analog AMP-PCP, suggesting that neither binding nor hydrolysis of ATP is required for RNA binding. Moreover, the K1236A mutant which was defective in binding ATP exhibited an unusually strong affinity for RNA duplex. These results suggest that the conserved motifs cooperatively constitute a large functional domain rather than act as individual domains with strictly independent functions, and that alteration of one motif affects functions of other motifs in a mutually interactive fashion.
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Affiliation(s)
- K H Min
- Department of Life Science and Biotechnology, Korea University, Seoul
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47
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Drouet C, Bouillet L, Csopaki F, Colomb MG. Hepatitis C virus NS3 serine protease interacts with the serpin C1 inhibitor. FEBS Lett 1999; 458:415-8. [PMID: 10570951 DOI: 10.1016/s0014-5793(99)01194-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Both NS3 protein (1007-1657) and its protease moiety (NS3p, 1027-1207) were able to interact in vitro with C1 Inhibitor (C1Inh) to give a 95-kDa Mr C1Inh cleavage product similar to that obtained upon proteolysis by complement protease C1s. High-Mr reaction products were also detected after incubation of C1Inh with NS3 but not with NS3p; they correspond to ester-bonded complexes from their hydroxylamine lability. Similar reactivity of NS3 was observed upon incubation with alpha2-antiplasmin. Serpin cleavage was prevented by treatment of NS3 with synthetic serine protease inhibitors. This interaction between viral NS3 and host serpins suggests that NS3 is likely to be controlled by infected cell protease inhibitors.
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Affiliation(s)
- C Drouet
- Jeune Equipe IAI, Université Joseph Fourier Grenoble, Laboratoire d'Immunologie, Hopital Sud, Echirolles, France.
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48
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Zhong W, Ingravallo P, Wright-Minogue J, Skelton A, Uss AS, Chase R, Yao N, Lau JY, Hong Z. Nucleoside triphosphatase and RNA helicase activities associated with GB virus B nonstructural protein 3. Virology 1999; 261:216-26. [PMID: 10497107 DOI: 10.1006/viro.1999.9871] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
GB virus B (GBV-B) is a positive-stranded RNA virus that belongs to the Flaviviridae family. This virus is closely related to hepatitis C virus (HCV) and causes acute hepatitis in tamarins (Saguinus species). Nonstructural protein 3 (NS3) of GBV-B contains sequence motifs predictive of three enzymatic activities: serine protease, nucleoside triphosphatase (NTPase), and RNA helicase. The N-terminal serine protease has been characterized and shown to share similar substrate specificity with the HCV NS3 protease. In this report, a full-length GBV-B NS3 protein was expressed in Escherichia coli and purified to homogeneity. This recombinant protein was shown to possess polynucleotide-stimulated NTPase and double-stranded RNA (dsRNA) unwinding activities. Both activities were abolished by a single amino acid substitution, from the Lys (K) residue in the conserved walker motif A (or Ia) "AXXXXGK(210)S" to an Ala (A), confirming that they are intrinsic to GBV-B NS3. Kinetic parameters (K(m) and k(cat)) for hydrolysis of various NTPs or dNTPs were obtained. The dsRNA unwinding activity depends on the presence of divalent metal ions and ATP and requires an RNA duplex substrate with 3' unpaired regions (RNAs with 5' unpaired regions only or with blunt ends are not suitable substrates for this enzyme). This indicates that GBV-B NS3 RNA helicase unwinds dsRNA in the 3' to 5' direction. Direct interaction of the GBV-B NS3 protein with a single-stranded RNA was established using a gel-based RNA bandshift assay. Finally, a homology model of GBV-B NS3 RNA helicase domain based on the 3-dimensional structure of the HCV NS3 helicase that shows a great similarity in overall structure and surface charge distribution between the two proteins was proposed.
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Affiliation(s)
- W Zhong
- Department of Antiviral Therapy, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, New Jersey 07033-0539, USA.
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49
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Sardana VV, Blue JT, Zugay-Murphy J, Sardana MK, Kuo LC. An uniquely purified HCV NS3 protease and NS4A(21-34) peptide form a highly active serine protease complex in peptide hydrolysis. Protein Expr Purif 1999; 16:440-7. [PMID: 10425166 DOI: 10.1006/prep.1999.1090] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The N-terminal domain of the hepatitis C virus (HCV) polyprotein containing the NS3 protease (residues 1027 to 1206) was expressed in Escherichia coli as a soluble protein under the control of the T7 promoter. The enzyme has been purified to homogeneity with cation exchange (SP-Sepharose HR) and heparin affinity chromatography in the absence of any detergent. The purified enzyme preparation was soluble and remained stable in solution for several weeks at 4 degrees C. The proteolytic activity of the purified enzyme was examined, also in the absence of detergents, using a peptide mimicking the NS4A/4B cleavage site of the HCV polyprotein. Hydrolysis of this substrate at the expected Cys-Ala scissile bond was catalyzed by the recombinant protease with a pseudo second-order rate constant (k(cat)/K(M)) of 205 and 196,000 M(-1) s(-1), respectively, in the absence and presence of a central hydrophobic region (sequence represented by residues 21 to 34) of the NS4A protein. The rate constant in the presence of NS4A peptide cofactor was two orders of magnitude greater than reported previously for the NS3 protease domain. A significantly higher activity of the NS3 protease-NS4A cofactor complex was also observed with a substrate mimicking the NS4B/5A site (k(cat)/K(M) of 5180 +/- 670 M(-1) s(-1)). Finally, the optimal formation of a complex between the NS3 protease domain and the cofactor NS4A was critical for the high proteolytic activity observed.
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Affiliation(s)
- V V Sardana
- Department of Antiviral Research, Merck Research Laboratories, West Point, Pennsylvania 19486-0004, USA.
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Zhu X, Kim JL, Newcomb JR, Rose PE, Stover DR, Toledo LM, Zhao H, Morgenstern KA. Structural analysis of the lymphocyte-specific kinase Lck in complex with non-selective and Src family selective kinase inhibitors. Structure 1999; 7:651-61. [PMID: 10404594 DOI: 10.1016/s0969-2126(99)80086-0] [Citation(s) in RCA: 188] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND The lymphocyte-specific kinase Lck is a member of the Src family of non-receptor tyrosine kinases. Lck catalyzes the initial phosphorylation of T-cell receptor components that is necessary for signal transduction and T-cell activation. On the basis of both biochemical and genetic studies, Lck is considered an attractive cell-specific target for the design of novel T-cell immunosuppressants. To date, the lack of detailed structural information on the mode of inhibitor binding to Lck has limited the discovery of novel Lck inhibitors. RESULTS We report here the high-resolution crystal structures of an activated Lck kinase domain in complex with three structurally distinct ATP-competitive inhibitors: AMP-PNP (a non-selective, non-hydrolyzable ATP analog); staurosporine (a potent but non-selective protein kinase inhibitor); and PP2 (a potent Src family selective protein tyrosine kinase inhibitor). Comparison of these structures reveals subtle but important structural changes at the ATP-binding site. Furthermore, PP2 is found to access a deep, hydrophobic pocket near the ATP-binding cleft of the enzyme; this binding pocket is not occupied by either AMP-PNP or staurosporine. CONCLUSIONS The potency of staurosporine against Lck derives in part from an induced movement of the glycine-rich loop of the enzyme upon binding of this ligand, which maximizes the van der Waals interactions present in the complex. In contrast, PP2 binds tightly and selectively to Lck and other Src family kinases by making additional contacts in a deep, hydrophobic pocket adjacent to the ATP-binding site; the amino acid composition of this pocket is unique to Src family kinases. The structures of these Lck complexes offer useful structural insights as they demonstrate that kinase selectivity can be achieved with small-molecule inhibitors that exploit subtle topological differences among protein kinases.
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Affiliation(s)
- X Zhu
- Kinetix Pharmaceuticals, Inc., Medford, MA 02155, USA.
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