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Prichard MN, Kern ER. Orthopoxvirus targets for the development of new antiviral agents. Antiviral Res 2012; 94:111-25. [PMID: 22406470 PMCID: PMC3773844 DOI: 10.1016/j.antiviral.2012.02.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 02/10/2012] [Accepted: 02/21/2012] [Indexed: 12/29/2022]
Abstract
Investments in the development of new drugs for orthopoxvirus infections have fostered new avenues of research, provided an improved understanding of orthopoxvirus biology and yielded new therapies that are currently progressing through clinical trials. These broad-based efforts have also resulted in the identification of new inhibitors of orthopoxvirus replication that target many different stages of viral replication cycle. This review will discuss progress in the development of new anti-poxvirus drugs and the identification of new molecular targets that can be exploited for the development of new inhibitors. The prototype of the orthopoxvirus group is vaccinia virus and its replication cycle will be discussed in detail noting specific viral functions and their associated gene products that have the potential to serve as new targets for drug development. Progress that has been achieved in recent years should yield new drugs for the treatment of these infections and might also reveal new approaches for antiviral drug development with other viruses.
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Affiliation(s)
- Mark N Prichard
- Department of Pediatrics, The University of Alabama at Birmingham, Birmingham, AL 35233-1711, United States.
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Gammon DB, Gowrishankar B, Duraffour S, Andrei G, Upton C, Evans DH. Vaccinia virus-encoded ribonucleotide reductase subunits are differentially required for replication and pathogenesis. PLoS Pathog 2010; 6:e1000984. [PMID: 20628573 PMCID: PMC2900304 DOI: 10.1371/journal.ppat.1000984] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Accepted: 06/03/2010] [Indexed: 11/19/2022] Open
Abstract
Ribonucleotide reductases (RRs) are evolutionarily-conserved enzymes that catalyze the rate-limiting step during dNTP synthesis in mammals. RR consists of both large (R1) and small (R2) subunits, which are both required for catalysis by the R12R22 heterotetrameric complex. Poxviruses also encode RR proteins, but while the Orthopoxviruses infecting humans [e.g. vaccinia (VACV), variola, cowpox, and monkeypox viruses] encode both R1 and R2 subunits, the vast majority of Chordopoxviruses encode only R2 subunits. Using plaque morphology, growth curve, and mouse model studies, we investigated the requirement of VACV R1 (I4) and R2 (F4) subunits for replication and pathogenesis using a panel of mutant viruses in which one or more viral RR genes had been inactivated. Surprisingly, VACV F4, but not I4, was required for efficient replication in culture and virulence in mice. The growth defects of VACV strains lacking F4 could be complemented by genes encoding other Chordopoxvirus R2 subunits, suggesting conservation of function between poxvirus R2 proteins. Expression of F4 proteins encoding a point mutation predicted to inactivate RR activity but still allow for interaction with R1 subunits, caused a dominant negative phenotype in growth experiments in the presence or absence of I4. Co-immunoprecipitation studies showed that F4 (as well as other Chordopoxvirus R2 subunits) form hybrid complexes with cellular R1 subunits. Mutant F4 proteins that are unable to interact with host R1 subunits failed to rescue the replication defect of strains lacking F4, suggesting that F4-host R1 complex formation is critical for VACV replication. Our results suggest that poxvirus R2 subunits form functional complexes with host R1 subunits to provide sufficient dNTPs for viral replication. Our results also suggest that R2-deficient poxviruses may be selective oncolytic agents and our bioinformatic analyses provide insights into how poxvirus nucleotide metabolism proteins may have influenced the base composition of these pathogens. Efficient genome replication is central to the virulence of all DNA viruses, including poxviruses. To ensure replication efficiency, many of the more virulent poxviruses encode their own nucleotide metabolism machinery, including ribonucleotide reductase (RR) enzymes, which act to provide ample DNA precursors for replication. RR enzymes require both large (R1) and small (R2) subunit proteins for activity. Curiously, some poxviruses only encode R2 subunits. Other poxviruses, such as the smallpox vaccine strain, vaccinia virus (VACV), encode both R1 and R2 subunits. We report here that the R2, but not the R1, subunit of VACV RR is required for efficient replication and virulence. We also provide evidence that several poxvirus R2 proteins form novel complexes with host R1 subunits and this interaction is required for efficient VACV replication in primate cells. Our study explains why some poxviruses only encode R2 subunits and identifies a role for these proteins in poxvirus pathogenesis. Furthermore, we provide evidence that mutant poxviruses unable to generate R2 proteins may become entirely dependent upon host RR activity. This may restrict their replication to cells that over-express RR proteins such as cancer cells, making them potential therapeutics for human malignancies.
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Affiliation(s)
- Don B. Gammon
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada
| | - Branawan Gowrishankar
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada
| | - Sophie Duraffour
- Laboratory of Virology and Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Graciela Andrei
- Laboratory of Virology and Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Chris Upton
- Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - David H. Evans
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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Smee DF, Humphreys DE, Hurst BL, Barnard DL. Antiviral activities and phosphorylation of 5-halo-2'-deoxyuridines and N-methanocarbathymidine in cells infected with vaccinia virus. Antivir Chem Chemother 2008; 19:15-24. [PMID: 18610554 DOI: 10.1177/095632020801900103] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND The antipoxviral activities and phosphorylation of N-methanocarbathymidine ([N]-MCT) and four 5-halo-2'-deoxyuridines, namely 5-fluoro-(FdU), 5-chloro-(CldU), 5-bromo-(BrdU), and 5-iodo-(IdU) derivatives, were explored. METHODS Antiviral activities and nucleoside metabolism were determined in C127I mouse, LLC-MK2 monkey, and A549 human cells infected with thymidine-kinase-containing and -deficient (TK+ and TK-) vaccinia (WR strain) viruses. RESULTS The antiviral potencies of CldU, BrdU and IdU were increased 16-26-fold in LLC-MK2 cells infected with TK+ compared with TK- virus infections, but enhancement of activity was much less in the other cell lines. (N)-MCT was nearly equally active against TK+ and TK- viruses in the three cell lines. Antiviral activity of FdU was associated with cytotoxicity. Uninfected and infected cells metabolized compounds to mono-, di- and triphosphates. The thymidine, BrdU and IdU triphosphate levels were higher in C127I and LLC-MK2 cells infected with TK+ than with TK- virus. (N)-MCT monophosphate levels were much higher in TK+ virus-infected cells, but without corresponding increases in (N)-MCT triphosphate. Furthermore, TK+ virus infections did not appreciably alter (N)-MCT triphosphate levels in other mouse (L929), monkey (MA-104 and Vero) and human cell lines (A549). Antiviral potency of the compounds was greater in C127I than in LLC-MK2 cells, yet lower intracellular triphosphate levels were found in C127I cells. CONCLUSION We conclude that viral TK plays an important role in increasing the antiviral potencies of these compounds in some cell lines, but minimally in others. These findings may have implications in treating infected animals with compounds that are dependent upon poxvirus TK for their activation, because viral TK activity may vary greatly due to cell type.
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Affiliation(s)
- Donald F Smee
- Institute for Antiviral Research, Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan, Utah, USA.
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Prichard MN, Keith KA, Johnson MP, Harden EA, McBrayer A, Luo M, Qiu S, Chattopadhyay D, Fan X, Torrence PF, Kern ER. Selective phosphorylation of antiviral drugs by vaccinia virus thymidine kinase. Antimicrob Agents Chemother 2007; 51:1795-803. [PMID: 17325220 PMCID: PMC1855528 DOI: 10.1128/aac.01447-06] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The antiviral activity of a new series of thymidine analogs was determined against vaccinia virus (VV), cowpox virus (CV), herpes simplex virus, and varicella-zoster virus. Several compounds were identified that had good activity against each of the viruses, including a set of novel 5-substituted deoxyuridine analogs. To investigate the possibility that these drugs might be phosphorylated preferentially by the viral thymidine kinase (TK) homologs, the antiviral activities of these compounds were also assessed using TK-deficient strains of some of these viruses. Some of these compounds were shown to be much less effective in the absence of a functional TK gene in CV, which was unexpected given the high degree of amino acid identity between this enzyme and its cellular homolog. This unanticipated result suggested that the CV TK was important in the mechanism of action of these compounds and also that it might phosphorylate a wider variety of substrates than other type II enzymes. To confirm these data, we expressed the VV TK and human TK1 in bacteria and isolated the purified enzymes. Enzymatic assays demonstrated that the viral TK could efficiently phosphorylate many of these compounds, whereas most of the compounds were very poor substrates for the cellular kinase, TK1. Thus, the specific phosphorylation of these compounds by the viral kinase may be sufficient to explain the TK dependence. This unexpected result suggests that selective phosphorylation by the viral kinase may be a promising new approach in the discovery of highly selective inhibitors of orthopoxvirus replication.
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Affiliation(s)
- Mark N Prichard
- Department of Pediatrics, University of Alabama School of Medicine, Birmingham, AL 35233, USA.
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Zhang X, Amer A, Fan X, Balzarini J, Neyts J, De Clercq E, Prichard M, Kern E, Torrence PF. Synthesis and antiviral activities of new acyclic and "double-headed" nucleoside analogues. Bioorg Chem 2006; 35:221-32. [PMID: 17270235 PMCID: PMC4265801 DOI: 10.1016/j.bioorg.2006.11.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Revised: 11/20/2006] [Accepted: 11/21/2006] [Indexed: 10/23/2022]
Abstract
To develop an understanding of the structure-activity relationships for the inhibition of orthopoxviruses by nucleoside analogues, a variety of novel chemical entities were synthesized. These included a series of pyrimidine 5-hypermodified acyclic nucleoside analogues based upon recently discovered new leads, and some previously unknown "double-headed" or "abbreviated" nucleosides. None of the synthetic products possessed significant activity against two representative orthopoxviruses; namely, vaccinia virus and cowpox virus. They were also devoid of significant activity against a battery of other DNA and RNA viruses. So far as the results with the orthopoxviruses and herpes viruses, the results may point to the necessity for nucleoside analogues 5'-phosphorylation for antiviral efficacy.
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Affiliation(s)
- Xinying Zhang
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ 86011-5698, USA
| | - Adel Amer
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ 86011-5698, USA
| | - Xuesen Fan
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ 86011-5698, USA
| | - Jan Balzarini
- Rega Institute for Medical Research, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
| | - Johan Neyts
- Rega Institute for Medical Research, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
| | - Erik De Clercq
- Rega Institute for Medical Research, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
| | - Mark Prichard
- Department of Pediatrics, University of Alabama School of Medicine, Birmingham, AL, USA
| | - Earl Kern
- Department of Pediatrics, University of Alabama School of Medicine, Birmingham, AL, USA
| | - Paul F. Torrence
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ 86011-5698, USA
- *Corresponding author. Fax: +1 928 523 8111
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Structure of vaccinia virus thymidine kinase in complex with dTTP: insights for drug design. BMC STRUCTURAL BIOLOGY 2006; 6:22. [PMID: 17062140 PMCID: PMC1636055 DOI: 10.1186/1472-6807-6-22] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Accepted: 10/24/2006] [Indexed: 11/23/2022]
Abstract
Background Development of countermeasures to bioterrorist threats such as those posed by the smallpox virus (variola), include vaccination and drug development. Selective activation of nucleoside analogues by virus-encoded thymidine (dThd) kinases (TK) represents one of the most successful strategies for antiviral chemotherapy as demonstrated for anti-herpes drugs. Vaccinia virus TK is a close orthologue of variola TK but also shares a relatively high sequence identity to human type 2 TK (hTK), thus achieving drug selectivity relative to the host enzyme is challenging. Results In order to identify any differences compared to hTK that may be exploitable in drug design, we have determined the crystal structure of VVTK, in complex with thymidine 5'-triphosphate (dTTP). Although most of the active site residues are conserved between hTK and VVTK, we observe a difference in conformation of residues Asp-43 and Arg-45. The equivalent residues in hTK hydrogen bond to dTTP, whereas in subunit D of VVTK, Asp-43 and Arg-45 adopt a different conformation preventing interaction with this nucleotide. Asp-43 and Arg-45 are present in a flexible loop, which is disordered in subunits A, B and C. The observed difference in conformation and flexibility may also explain the ability of VVTK to phosphorylate (South)-methanocarbathymine whereas, in contrast, no substrate activity with hTK is reported for this compound. Conclusion The difference in conformation for Asp-43 and Arg-45 could thus be used in drug design to generate VVTK/Variola TK-selective nucleoside analogue substrates and/or inhibitors that have lower affinity for hTK.
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Fan X, Zhang X, Zhou L, Keith KA, Prichard MN, Kern ER, Torrence PF. Toward orthopoxvirus countermeasures: a novel heteromorphic nucleoside of unusual structure. J Med Chem 2006; 49:4052-4. [PMID: 16821766 PMCID: PMC4298854 DOI: 10.1021/jm060404n] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Two privileged drug scaffolds have been hybridized to create the novel heteromorphic nucleoside 5-(2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-chromen-4-yl)-1-(2-deoxypentofuranosyl)pyrimidine-2,4(1H,3H)-dione (2). Compound 2 inhibited the replication of two orthopoxviruses, vaccinia virus (VV) (EC(50) = 4.6 +/- 2.0 microM), and cowpox virus (CV) (EC(50) = 2.0 +/- 0.3 microM). Compound 2 exhibited reduced activity against a thymidine kinase (TK) negative strain of CV, implying a requirement for 5'-monophosphorylation for antiorthopoxvirus activity. Compound 2 was efficiently phosphorylated by VV TK, establishing that VV TK is more promiscuous than previously believed.
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Affiliation(s)
| | | | | | | | | | | | - Paul F. Torrence
- To whom correspondence should be addressed. Phone: 928-523-0298. Fax: 928-523-8111.
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Prichard MN, Keith KA, Quenelle DC, Kern ER. Activity and mechanism of action of N-methanocarbathymidine against herpesvirus and orthopoxvirus infections. Antimicrob Agents Chemother 2006; 50:1336-41. [PMID: 16569849 PMCID: PMC1426929 DOI: 10.1128/aac.50.4.1336-1341.2006] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
N-Methanocarbathymidine [(N)-MCT] is a conformationally locked nucleoside analog that is active against some herpesviruses and orthopoxviruses in vitro. The antiviral activity of this molecule is dependent on the type I thymidine kinase (TK) in herpes simplex virus and also appears to be dependent on the type II TK expressed by cowpox and vaccinia viruses, suggesting that it is a substrate for both of these divergent forms of the enzyme. The drug is also a good inhibitor of viral DNA synthesis in both viruses and is consistent with inhibition of the viral DNA polymerase once it is activated by the viral TK homologs. This mechanism of action explains the rather unusual spectrum of activity, which is limited to orthopoxviruses, alphaherpesviruses, and Epstein-Barr virus, since these viruses express molecules with TK activity that can phosphorylate and thus activate the drug. The compound is also effective in vivo and reduces the mortality of mice infected with orthopoxviruses, as well as those infected with herpes simplex virus type 1 when treatment is initiated 24 h after infection. These results indicate that (N)-MCT is active in vitro and in vivo, and its mechanism of action suggests that the molecule may be an effective therapeutic for orthopoxvirus and herpesvirus infections, thus warranting further development.
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Affiliation(s)
- Mark N Prichard
- Department of Pediatrics, University of Alabama School of Medicine, Birmingham, AL 35233, USA.
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Prichard MN, Williams AD, Keith KA, Harden EA, Kern ER. Distinct thymidine kinases encoded by cowpox virus and herpes simplex virus contribute significantly to the differential antiviral activity of nucleoside analogs. Antiviral Res 2006; 71:1-6. [PMID: 16530858 DOI: 10.1016/j.antiviral.2006.01.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2005] [Revised: 01/19/2006] [Accepted: 01/19/2006] [Indexed: 11/21/2022]
Abstract
Orthopoxviruses and herpesviruses are both large enveloped DNA viruses, yet these virus families exhibit very different susceptibilities to antiviral drugs. We investigated the activation of nucleoside analogs by the types I and II thymidine kinase (TK) homologs expressed by herpes simplex virus type 1 (HSV-1) and cowpox virus (CV). Antiviral activity against TK(-) and TK(+) strains of HSV-1 and CV was determined, and the ratio of the EC(50) values was used as a measurement of TK dependence. As to HSV-1, most of the selected compounds were markedly less effective against the TK(-) strains, suggesting that this enzyme was required for the activation of these nucleoside analogs. This differs from the results for CV where only idoxuridine and bromodeoxyuridine appeared to be activated, putatively by the type II TK expressed by this virus. These data confirm that the type II TK encoded by CV exhibits a more limited substrate specificity than the type I TK encoded by HSV-1. These data suggest that the inefficient activation of nucleoside analogs by the orthopoxvirus TK significantly limits their activity. Additional screening against orthopoxviruses will be required to identify nucleoside analogs that are efficiently activated by their type II TK.
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Affiliation(s)
- Mark N Prichard
- University of Alabama School of Medicine, Department of Pediatrics, Birmingham, 35233, USA.
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Affiliation(s)
- M E Black
- Department of Pharmaceutical Sciences, P.O. Box 646534, Washington State University, Pullman, WA 99164-6534, USA
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Sutterluety H, Seiser C. Thymidine inhibits the growth-arrest-specific degradation of thymidine kinase protein in transfected L fibroblasts. J Mol Biol 1997; 265:153-60. [PMID: 9020979 DOI: 10.1006/jmbi.1996.0721] [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: 02/03/2023]
Abstract
The expression of murine thymidine kinase (TK) is strictly dependent on the growth state of the cell. Expressing epitope-tagged TK in LTK cells, we have previously shown that low TK enzyme levels in G0 cells are in part due to a dramatic decrease in TK protein stability. Here we report that thymidine, one of the substrates of TK, is able to counteract the growth-arrest-specific decrease of TK expression. While TK mRNA levels and TK translation rate are almost unaffected by thymidine, the TK protein half-life rose more than sixfold after addition of the nucleoside to resting cells. The effect of thymidine is reversible and is independent of its presence during the protein synthesis of TK. Dideoxythymidine, a specific inhibitor of the TK enzyme activity, also has the capacity to increase TK protein levels in G0 cells, indicating that the substrate itself exerts the stabilising effect on the TK protein.
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Affiliation(s)
- H Sutterluety
- Institute of Molecular Biology, University of Vienna, Austria
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Brown DG, Visse R, Sandhu G, Davies A, Rizkallah PJ, Melitz C, Summers WC, Sanderson MR. Crystal structures of the thymidine kinase from herpes simplex virus type-1 in complex with deoxythymidine and ganciclovir. NATURE STRUCTURAL BIOLOGY 1995; 2:876-81. [PMID: 7552712 DOI: 10.1038/nsb1095-876] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The crystal structures of thymidine kinase from herpes simplex virus type-1 complexed with its natural substrate deoxythymidine (dT) and complexed with the guanosine analogue Ganciclovir have been solved. Both structures are in the C222(1) crystal form with two molecules per asymmetric unit related by a non-crystallographic two-fold axis. The present models have been refined to 2.8 A and 2.2 A, with crystallographic R factors of 24.1% and 23.3% for the dT and Ganciclovir complexes respectively, without the inclusion of any solvent molecules. The core of the molecule exhibits high structural homology with adenylate kinase and other nucleotide binding proteins. These structural similarities provide an insight into the mechanism of nucleoside phosphorylation by thymidine kinase.
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Affiliation(s)
- D G Brown
- Division of Biomedical Sciences, Randall Institute, King's College, London, UK
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Rechtin TM, Black ME, Mao F, Lewis ML, Drake RR. Purification and photoaffinity labeling of herpes simplex virus type-1 thymidine kinase. J Biol Chem 1995; 270:7055-60. [PMID: 7706243 DOI: 10.1074/jbc.270.13.7055] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The molecular basis for the treatment of human herpesviruses with nucleoside drugs is the phosphorylation of these drugs by the viral-encoded thymidine kinases. In order to better understand the structural and enzymatic mechanisms by which herpesviral thymidine kinases recognize their substrates, photoaffinity labeling with [alpha-32P]5-azido-2'-deoxyuridine-5'-monophosphate and [ gamma-32P]8-azidoadenosine-5'-triphosphate was used to characterize the thymidine, thymidylate, and ATP active sites of the herpes simplex virus-1 (HSV-1) thymidine kinase. For this study, HSV-1 thymidine kinase and a site-specific mutant enzyme (C336Y, known to confer acyclovir resistance) were expressed in bacteria and purified by a rapid, two-step protocol. The specificity of photoaffinity labeling of these HSV-1 thymidine kinases was demonstrated by the ability of site-directed substrates such as thymidine, thymidylate, acyclovir, 5-bromovinyl-2'-deoxyuridine, and ATP to inhibit photoinsertion. Differences in inhibition patterns of photoaffinity labeling correlated with kinetic differences between the wild-type and C336Y HSV-1 thymidine kinases. Cumulative results suggest that the acyclovir-resistant cysteine 336 mutation primarily affects the ATP binding site; yet it also leads to alteration in the binding affinity of nucleoside drugs in the thymidine site. In this study, azidonucleotide photoaffinity analogs are shown to be effective tools for studying the active-site environment of HSV-1 thymidine kinase and related site-specific mutants.
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Affiliation(s)
- T M Rechtin
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA
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Black ME, Loeb LA. Identification of important residues within the putative nucleoside binding site of HSV-1 thymidine kinase by random sequence selection: analysis of selected mutants in vitro. Biochemistry 1993; 32:11618-26. [PMID: 8218229 DOI: 10.1021/bi00094a019] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Random sequence mutagenesis in conjunction with genetic complementation was used to map the function of amino acid residues within the putative nucleoside binding site of the herpes simplex virus type 1 (HSV-1) thymidine kinase (TK). Six codons of the putative nucleoside binding site of the HSV-1 tk were substituted by a duplex of extended oligonucleotides containing 20% random sequences. Approximately 260 mutants were screened for the ability to genetically complement a TK-deficient Escherichia coli. Of those screened, 32% conferred TK activity. Approximately 60% of the TK positive clones contained single amino acid changes, 23% contained double changes, and 13.4% encoded the wild-type TK amino acid sequence. A small percentage of clones, 2.4% and 1.2%, contained triple or quadruple alterations, respectively. Three residues (D162, H163, and R164) appeared to be highly conserved especially with regard to the type of residues able to substitute. Secondary screening results indicated that several of the mutants had higher affinities for acyclovir and/or 3'-azido-3'-deoxythymidine than thymidine in complementation assays. In addition, a number of clones were unable to form colonies on selection medium at elevated temperatures (42 degrees C). Eight selected mutants were subcloned into an in vitro transcription vector and the derived transcripts used to program a rabbit reticulocyte lysate cell-free translation system. Biologically active translation products were then analyzed in vitro for thymidine kinase activity, for thermal stability, and for the ability to phosphorylate selected nucleoside analogues. Two of the eight mutants had an elevated thymidine kinase activity, two were significantly thermolabile, and three exhibited enhanced efficiency in phosphorylation of nucleoside analogues.
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Affiliation(s)
- M E Black
- Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology, School of Medicine, University of Washington, Seattle 98195
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Xu Y, Plunkett W. Regulation of thymidine kinase and thymidylate synthase in intact human lymphoblast CCRF-CEM cells. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41537-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Abstract
Thymidine kinases were described for cellular life long before it was shown that they could also be encoded by viruses, but the viral thymidine kinase genes were the first to be sequenced. These enzymes have been extraordinarily useful to the researcher, serving first to help label DNA, then to get thymidine analogs incorporated into DNA for therapeutic and other purposes and more recently to move genes from one genome to another. Knowledge of the nucleotide and amino acid sequences of these enzymes has allowed some deductions about their possible three-dimensional structure, as well as the location on the polypeptide of various functions; it has also allowed their classification into two main groups: the herpesviral thymidine/eukaryotic deoxycytidine kinases and the poxviral and cellular thymidine kinases; the relationships of the mitochondrial enzyme are still not clear.
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Affiliation(s)
- G A Gentry
- Department of Microbiology, University of Mississippi Medical Center, Jackson 39216-4505
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