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Abstract
Phosphoryl transfer plays key roles in signaling, energy transduction, protein synthesis, and maintaining the integrity of the genetic material. On the surface, it would appear to be a simple nucleophile displacement reaction. However, this simplicity is deceptive, as, even in aqueous solution, the low-lying d-orbitals on the phosphorus atom allow for eight distinct mechanistic possibilities, before even introducing the complexities of the enzyme catalyzed reactions. To further complicate matters, while powerful, traditional experimental techniques such as the use of linear free-energy relationships (LFER) or measuring isotope effects cannot make unique distinctions between different potential mechanisms. A quarter of a century has passed since Westheimer wrote his seminal review, 'Why Nature Chose Phosphate' (Science 235 (1987), 1173), and a lot has changed in the field since then. The present review revisits this biologically crucial issue, exploring both relevant enzymatic systems as well as the corresponding chemistry in aqueous solution, and demonstrating that the only way key questions in this field are likely to be resolved is through careful theoretical studies (which of course should be able to reproduce all relevant experimental data). Finally, we demonstrate that the reason that nature really chose phosphate is due to interplay between two counteracting effects: on the one hand, phosphates are negatively charged and the resulting charge-charge repulsion with the attacking nucleophile contributes to the very high barrier for hydrolysis, making phosphate esters among the most inert compounds known. However, biology is not only about reducing the barrier to unfavorable chemical reactions. That is, the same charge-charge repulsion that makes phosphate ester hydrolysis so unfavorable also makes it possible to regulate, by exploiting the electrostatics. This means that phosphate ester hydrolysis can not only be turned on, but also be turned off, by fine tuning the electrostatic environment and the present review demonstrates numerous examples where this is the case. Without this capacity for regulation, it would be impossible to have for instance a signaling or metabolic cascade, where the action of each participant is determined by the fine-tuned activity of the previous piece in the production line. This makes phosphate esters the ideal compounds to facilitate life as we know it.
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52
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Thiyagarajan A, Salim MT, Balaraju T, Bal C, Baba M, Sharon A. Structure based medicinal chemistry approach to develop 4-methyl-7-deazaadenine carbocyclic nucleosides as anti-HCV agent. Bioorg Med Chem Lett 2012; 22:7742-7. [DOI: 10.1016/j.bmcl.2012.09.072] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 09/16/2012] [Accepted: 09/19/2012] [Indexed: 11/30/2022]
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53
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Sainsbury S, Niesser J, Cramer P. Structure and function of the initially transcribing RNA polymerase II-TFIIB complex. Nature 2012; 493:437-40. [PMID: 23151482 DOI: 10.1038/nature11715] [Citation(s) in RCA: 142] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 10/26/2012] [Indexed: 01/24/2023]
Abstract
The general transcription factor (TF) IIB is required for RNA polymerase (Pol) II initiation and extends with its B-reader element into the Pol II active centre cleft. Low-resolution structures of the Pol II-TFIIB complex indicated how TFIIB functions in DNA recruitment, but they lacked nucleic acids and half of the B-reader, leaving other TFIIB functions enigmatic. Here we report crystal structures of the Pol II-TFIIB complex from the yeast Saccharomyces cerevisiae at 3.4 Å resolution and of an initially transcribing complex that additionally contains the DNA template and a 6-nucleotide RNA product. The structures reveal the entire B-reader and protein-nucleic acid interactions, and together with functional data lead to a more complete understanding of transcription initiation. TFIIB partially closes the polymerase cleft to position DNA and assist in its opening. The B-reader does not reach the active site but binds the DNA template strand upstream to assist in the recognition of the initiator sequence and in positioning the transcription start site. TFIIB rearranges active-site residues, induces binding of the catalytic metal ion B, and stimulates initial RNA synthesis allosterically. TFIIB then prevents the emerging DNA-RNA hybrid duplex from tilting, which would impair RNA synthesis. When the RNA grows beyond 6 nucleotides, it is separated from DNA and is directed to its exit tunnel by the B-reader loop. Once the RNA grows to 12-13 nucleotides, it clashes with TFIIB, triggering TFIIB displacement and elongation complex formation. Similar mechanisms may underlie all cellular transcription because all eukaryotic and archaeal RNA polymerases use TFIIB-like factors, and the bacterial initiation factor sigma has TFIIB-like topology and contains the loop region 3.2 that resembles the B-reader loop in location, charge and function. TFIIB and its counterparts may thus account for the two fundamental properties that distinguish RNA from DNA polymerases: primer-independent chain initiation and product separation from the template.
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Affiliation(s)
- Sarah Sainsbury
- Gene Center and Department of Biochemistry, Center for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany
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Bera M, Curtiss ABS, Musie GT, Powell DR. New Dinuclear Cobalt(II) and Zinc(II) Complexes of a Carboxylate-Rich Dinucleating Ligand: Synthesis, Structure, Spectroscopic Characterization, and Their Interactions with Sugars. Inorg Chem 2012; 51:12093-101. [DOI: 10.1021/ic3004432] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Manindranath Bera
- Department of Chemistry, University of Kalyani, Kalyani, West Bengal 741235,
India
| | - Ashley B. S. Curtiss
- Department of Chemistry, The University of Texas at San Antonio, San Antonio,
Texas 78249, United States
| | - Ghezai T. Musie
- Department of Chemistry, The University of Texas at San Antonio, San Antonio,
Texas 78249, United States
| | - Douglas R. Powell
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United
States
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55
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Giraut A, Abu El-Asrar R, Marlière P, Delarue M, Herdewijn P. 2'-Deoxyribonucleoside phosphoramidate triphosphate analogues as alternative substrates for E. coli polymerase III. Chembiochem 2012; 13:2439-44. [PMID: 23023962 DOI: 10.1002/cbic.201200413] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Indexed: 01/27/2023]
Abstract
Thermostable bacterial polymerases like Taq, Therminator and Vent exo(-) are able to perform DNA synthesis by using modified DNA precursors, a property that is exploited in several therapeutic and biotechnological applications. Viral polymerases are also known to accept modified substrates, and this has proven crucial in the development of antiviral therapies. However, non-thermostable polymerases of bacterial origin, or engineered variants, that have similar substrate tolerance and could be used for synthetic biology purposes remain to be identified. We have identified the α subunit of Escherichia coli polymerase III (Pol III α) as a bacterial polymerase that is able to recognise and process as substrates several pyrophosphate-modified dATP analogues in place of its natural substrate dATP for template-directed DNA synthesis. A number of dATP analogues featuring a modified pyrophosphate group were able to serve as substrates during enzymatic DNA synthesis by Pol III α. Features such as the presence of potentially chelating chemical groups and the size and spatial flexibility of the chemical structure seem to be of major importance for the modified leaving group to play its role during the enzymatic reaction. In addition, we could establish that if the pyrophosphate group is altered, deoxynucleotide incorporation proceeds with an efficiency varying with the nature of the nucleobase. Our results represent a great step towards the achievement of a system of artificial DNA synthesis hosted by E. coli and involving the use of altered nucleotide precursors for nucleic acid synthesis.
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Affiliation(s)
- Anne Giraut
- Katholieke Universiteit Leuven, Rega Institute, Laboratory for Medicinal Chemistry, Minderbroedersstraat 10, 3000 Leuven, Belgium
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56
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Kaplan CD. Basic mechanisms of RNA polymerase II activity and alteration of gene expression in Saccharomyces cerevisiae. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:39-54. [PMID: 23022618 DOI: 10.1016/j.bbagrm.2012.09.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 09/18/2012] [Accepted: 09/20/2012] [Indexed: 01/12/2023]
Abstract
Transcription by RNA polymerase II (Pol II), and all RNA polymerases for that matter, may be understood as comprising two cycles. The first cycle relates to the basic mechanism of the transcription process wherein Pol II must select the appropriate nucleoside triphosphate (NTP) substrate complementary to the DNA template, catalyze phosphodiester bond formation, and translocate to the next position on the DNA template. Performing this cycle in an iterative fashion allows the synthesis of RNA chains that can be over one million nucleotides in length in some larger eukaryotes. Overlaid upon this enzymatic cycle, transcription may be divided into another cycle of three phases: initiation, elongation, and termination. Each of these phases has a large number of associated transcription factors that function to promote or regulate the gene expression process. Complicating matters, each phase of the latter transcription cycle are coincident with cotranscriptional RNA processing events. Additionally, transcription takes place within a highly dynamic and regulated chromatin environment. This chromatin environment is radically impacted by active transcription and associated chromatin modifications and remodeling, while also functioning as a major platform for Pol II regulation. This review will focus on our basic knowledge of the Pol II transcription mechanism, and how altered Pol II activity impacts gene expression in vivo in the model eukaryote Saccharomyces cerevisiae. This article is part of a Special Issue entitled: RNA Polymerase II Transcript Elongation.
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Affiliation(s)
- Craig D Kaplan
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA.
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57
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Martinez-Rucobo FW, Cramer P. Structural basis of transcription elongation. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:9-19. [PMID: 22982352 DOI: 10.1016/j.bbagrm.2012.09.002] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 09/06/2012] [Accepted: 09/07/2012] [Indexed: 01/13/2023]
Abstract
For transcription elongation, all cellular RNA polymerases form a stable elongation complex (EC) with the DNA template and the RNA transcript. Since the millennium, a wealth of structural information and complementary functional studies provided a detailed three-dimensional picture of the EC and many of its functional states. Here we summarize these studies that elucidated EC structure and maintenance, nucleotide selection and addition, translocation, elongation inhibition, pausing and proofreading, backtracking, arrest and reactivation, processivity, DNA lesion-induced stalling, lesion bypass, and transcriptional mutagenesis. In the future, additional structural and functional studies of elongation factors that control the EC and their possible allosteric modes of action should result in a more complete understanding of the dynamic molecular mechanisms underlying transcription elongation. This article is part of a Special Issue entitled: RNA polymerase II Transcript Elongation.
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58
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Rymer RU, Solorio FA, Tehranchi AK, Chu C, Corn JE, Keck JL, Wang JD, Berger JM. Binding mechanism of metal⋅NTP substrates and stringent-response alarmones to bacterial DnaG-type primases. Structure 2012; 20:1478-89. [PMID: 22795082 PMCID: PMC3438381 DOI: 10.1016/j.str.2012.05.017] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2012] [Revised: 05/17/2012] [Accepted: 05/25/2012] [Indexed: 11/30/2022]
Abstract
Primases are DNA-dependent RNA polymerases found in all cellular organisms. In bacteria, primer synthesis is carried out by DnaG, an essential enzyme that serves as a key component of DNA replication initiation, progression, and restart. How DnaG associates with nucleotide substrates and how certain naturally prevalent nucleotide analogs impair DnaG function are unknown. We have examined one of the earliest stages in primer synthesis and its control by solving crystal structures of the S. aureus DnaG catalytic core bound to metal ion cofactors and either individual nucleoside triphosphates or the nucleotidyl alarmones, pppGpp and ppGpp. These structures, together with both biochemical analyses and comparative studies of enzymes that use the same catalytic fold as DnaG, pinpoint the predominant nucleotide-binding site of DnaG and explain how the induction of the stringent response in bacteria interferes with primer synthesis.
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Affiliation(s)
- Richard U Rymer
- California Institute for Quantitative Biosciences, 374D Stanley Hall #3220, University of California, Berkeley, Berkeley, CA 94720-3220, USA
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59
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Yang S, Herdewijn P. Polymerase-dependent DNA synthesis from phosphoramidate-activated nucleotides. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2011; 30:597-608. [PMID: 21888550 DOI: 10.1080/15257770.2011.598491] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Nucleoside triphosphate mimetics, which are substrates for polymerases, can be used in the enzymatic synthesis of nucleic acids. Alternatively, they might also become reversible or irreversible enzyme inhibitors. In order to analyze the effects of 5'-phosphoramidate modification of deoxynucleotide in DNA synthesis, 3-phosphono-L-Ala-dNMP (N = A, T, or G) were evaluated as substrates of HIV-1 RT, Vent (exo(-)), and Therminator polymerase, respectively. The DNA-dependent DNA polymerase activity is significantly higher for Vent exo(-) polymerase than for HIV-1 RT, which is reflected by the capacity of Vent exo(-) polymerase to efficiently synthesize DNA without stalling effects. In addition, Vent (exo(-)) polymerase proved to be more accurate than Therminator polymerase, based on Watson-Crick base-pairing. The optimal yield (88%-97%) of full-length elongation can be obtained in 60 minutes by Vent (exo(-)) polymerase at 0.025 U/μL, with the phosphoramidate analogues as substrates. These data led us to conclude that the optimal pyrophosphate mimetic for the enzyme-catalyzed synthesis of DNA is polymerase dependent.
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Affiliation(s)
- Shiqiong Yang
- Laboratory of Medicinal Chemistry, Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium
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60
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Kirby TW, DeRose EF, Cavanaugh NA, Beard WA, Shock DD, Mueller GA, Wilson SH, London RE. Metal-induced DNA translocation leads to DNA polymerase conformational activation. Nucleic Acids Res 2011; 40:2974-83. [PMID: 22169953 PMCID: PMC3326329 DOI: 10.1093/nar/gkr1218] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Binding of the catalytic divalent ion to the ternary DNA polymerase β/gapped DNA/dNTP complex is thought to represent the final step in the assembly of the catalytic complex and is consequently a critical determinant of replicative fidelity. We have analyzed the effects of Mg2+ and Zn2+ on the conformational activation process based on NMR measurements of [methyl-13C]methionine DNA polymerase β. Unexpectedly, both divalent metals were able to produce a template base-dependent conformational activation of the polymerase/1-nt gapped DNA complex in the absence of a complementary incoming nucleotide, albeit with different temperature thresholds. This conformational activation is abolished by substituting Glu295 with lysine, thereby interrupting key hydrogen bonds necessary to stabilize the closed conformation. These and other results indicate that metal-binding can promote: translocation of the primer terminus base pair into the active site; expulsion of an unpaired pyrimidine, but not purine, base from the template-binding pocket; and motions of polymerase subdomains that close the active site. We also have performed pyrophosphorolysis studies that are consistent with predictions based on these results. These findings provide new insight into the relationships between conformational activation, enzyme activity and polymerase fidelity.
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Affiliation(s)
- Thomas W Kirby
- Laboratory of Structural Biology, NIEHS, Research Triangle Park, NC 27709, USA
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61
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Xia S, Wang M, Blaha G, Konigsberg WH, Wang J. Structural insights into complete metal ion coordination from ternary complexes of B family RB69 DNA polymerase. Biochemistry 2011; 50:9114-24. [PMID: 21923197 PMCID: PMC3760225 DOI: 10.1021/bi201260h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We have captured a preinsertion ternary complex of RB69 DNA polymerase (RB69pol) containing the 3' hydroxyl group at the terminus of an extendable primer (ptO3') and a nonhydrolyzable 2'-deoxyuridine 5'-α,β-substituted triphosphate, dUpXpp, where X is either NH or CH(2), opposite a complementary templating dA nucleotide residue. Here we report four structures of these complexes formed by three different RB69pol variants with catalytically inert Ca(2+) and four other structures with catalytically competent Mn(2+) or Mg(2+). These structures provide new insights into why the complete divalent metal-ion coordination complexes at the A and B sites are required for nucleotidyl transfer. They show that the metal ion in the A site brings ptO3' close to the α-phosphorus atom (Pα) of the incoming dNTP to enable phosphodiester bond formation through simultaneous coordination of both ptO3' and the nonbridging Sp oxygen of the dNTP's α-phosphate. The coordination bond length of metal ion A as well as its ionic radius determines how close ptO3' can approach Pα. These variables are expected to affect the rate of bond formation. The metal ion in the B site brings the pyrophosphate product close enough to Pα to enable pyrophosphorolysis and assist in the departure of the pyrophosphate. In these dUpXpp-containing complexes, ptO3' occupies the vertex of a distorted metal ion A coordination octahedron. When ptO3' is placed at the vertex of an undistorted, idealized metal ion A octahedron, it is within bond formation distance to Pα. This geometric relationship appears to be conserved among DNA polymerases of known structure.
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Affiliation(s)
- Shuangluo Xia
- Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT96520-8114, USA
| | - Mina Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT96520-8114, USA
| | - Gregor Blaha
- Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT96520-8114, USA
| | - William H. Konigsberg
- Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT96520-8114, USA
| | - Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT96520-8114, USA,Corresponding Author: Jimin Wang, Phone: (203)-432-5737; Fax: (203)-432-3282.
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62
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Balbo PB, Wang ECW, Tsai MD. Kinetic mechanism of active site assembly and chemical catalysis of DNA polymerase β. Biochemistry 2011; 50:9865-75. [PMID: 22010960 DOI: 10.1021/bi200954r] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has been inferred from structural and computational studies that the mechanism of DNA polymerases involves subtle but important discrete steps that occur between binding and recognition of the correct dNTP and chemical catalysis. These steps potentially include local conformational changes involving active site residues, reorganization of Mg(2+)-coordinating ligands, and proton transfer. Here we address this broad issue by conducting extensive transient state kinetic analyses of DNA polymerase β (Pol β). We also performed kinetic simulations to evaluate alternative kinetic models. These studies provide some support for two-step subdomain closing and define constraints under which a kinetically significant prechemistry step can occur. To experimentally identify additional microscopic steps, we developed a stopped flow absorbance assay to measure proton formation that occurs during catalysis. These studies provide direct evidence that formation of the enzyme-bound 3'-O(-) nucleophile is rate determining for chemistry. We additionally show that at low pH the chemical step is rate limiting for catalysis, but at high pH, a postchemistry conformational step is rate limiting due to a pH-dependent increase in the rate of nucleotidyl transfer. Finally, we performed exhaustive analyses of [Mg(2+)] and pH effects. In contrast to published studies, the results suggest an irregular pH dependence of k(pol), which is consistent with general base catalysis involving cooperativity between two or more protonic residues. Overall, the results represent significant advancement in the kinetic mechanism of Pol β and also reconcile some computational and experimental findings.
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Affiliation(s)
- Paul B Balbo
- Institute of Biological Chemistry, Academia Sinica, Nangang, Taipei 115, Taiwan
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63
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Abstract
Evolution balances DNA replication speed and accuracy to optimize replicative fitness and genetic stability. There is no selective pressure to improve DNA replication fidelity beyond the background mutation rate from other sources, such as DNA damage. However, DNA polymerases remain amenable to amino acid substitutions that lower intrinsic error rates. Here, we review these 'antimutagenic' changes in DNA polymerases and discuss what they reveal about mechanisms of replication fidelity. Pioneering studies with bacteriophage T4 DNA polymerase (T4 Pol) established the paradigm that antimutator amino acid substitutions reduce replication errors by increasing proofreading efficiency at the expense of polymerase processivity. The discoveries of antimutator substitutions in proofreading-deficient 'mutator' derivatives of bacterial Pols I and III and yeast Pol δ suggest there must be additional antimutagenic mechanisms. Remarkably, many of the affected amino acid positions from Pol I, Pol III, and Pol δ are similar to the original T4 Pol substitutions. The locations of antimutator substitutions within DNA polymerase structures suggest that they may increase nucleotide selectivity and/or promote dissociation of primer termini from polymerases poised for misincorporation, leading to expulsion of incorrect nucleotides. If misincorporation occurs, enhanced primer dissociation from polymerase domains may improve proofreading in cis by an intrinsic exonuclease or in trans by alternate cellular proofreading activities. Together, these studies reveal that natural selection can readily restore replication error rates to sustainable levels following an adaptive mutator phenotype.
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Affiliation(s)
- Alan J Herr
- Department of Pathology, University of Washington, Seattle, USA
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64
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Lestienne PP. Priming DNA replication from triple helix oligonucleotides: possible threestranded DNA in DNA polymerases. Mol Biol Int 2011; 2011:562849. [PMID: 22229092 PMCID: PMC3200174 DOI: 10.4061/2011/562849] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 07/02/2011] [Indexed: 11/20/2022] Open
Abstract
Triplex associate with a duplex DNA presenting the same polypurine or polypyrimidine-rich sequence in an antiparallel orientation. So far, triplex forming oligonucleotides (TFOs) are known to inhibit transcription, replication, and to induce mutations. A new property of TFO is reviewed here upon analysis of DNA breakpoint yielding DNA rearrangements; the synthesized sequence of the first direct repeat displays a skewed polypurine- rich sequence. This synthesized sequence can bind the second homologous duplex sequence through the formation of a triple helix, which is able to prime further DNA replication. In these case, the d(G)-rich Triple Helix Primers (THP) bind the homologous strand in a parallel manner, possibly via a RecA-like mechanism. This novel property is shared by all tested DNA polymerases: phage, retrovirus, bacteria, and human. These features may account for illegitimate initiation of replication upon single-strand breakage and annealing to a homologous sequence where priming may occur. Our experiments suggest that DNA polymerases can bind three instead of two polynucleotide strands in their catalytic centre.
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Affiliation(s)
- Patrick P Lestienne
- U 1053 INSERM, Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux, France
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65
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Structural and binding analysis of pyrimidinol carboxylic acid and N-hydroxy quinazolinedione HIV-1 RNase H inhibitors. Antimicrob Agents Chemother 2011; 55:2905-15. [PMID: 21464257 PMCID: PMC3101433 DOI: 10.1128/aac.01594-10] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
HIV-1 RNase H breaks down the intermediate RNA-DNA hybrids during reverse transcription, requiring two divalent metal ions for activity. Pyrimidinol carboxylic acid and N-hydroxy quinazolinedione inhibitors were designed to coordinate the two metal ions in the active site of RNase H. High-resolution (1.4 Å to 2.1 Å) crystal structures were determined with the isolated RNase H domain and reverse transcriptase (RT), which permit accurate assessment of the metal and water environment at the active site. The geometry of the metal coordination suggests that the inhibitors mimic a substrate state prior to phosphodiester catalysis. Surface plasmon resonance studies confirm metal-dependent binding to RNase H and demonstrate that the inhibitors do not bind at the polymerase active site of RT. Additional evaluation of the RNase H site reveals an open protein surface with few additional interactions to optimize active-site inhibitors.
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66
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Martínez L, Malliavin TE, Blondel A. Mechanism of reactant and product dissociation from the anthrax edema factor: a locally enhanced sampling and steered molecular dynamics study. Proteins 2011; 79:1649-61. [PMID: 21425348 DOI: 10.1002/prot.22991] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Revised: 12/14/2010] [Accepted: 12/30/2010] [Indexed: 11/07/2022]
Abstract
The anthrax edema factor is a toxin overproducing damaging levels of cyclic adenosine monophosphate (cAMP) and pyrophosphate (PPi) from ATP. Here, mechanisms of dissociation of ATP and products (cAMP, PPi) from the active site are studied using locally enhanced sampling (LES) and steered molecular dynamics simulations. Various substrate conformations and ionic binding modes found in crystallographic structures are considered. LES simulations show that PPi and cAMP dissociate through different solvent accessible channels, while ATP dissociation requires significant active site exposure to solvent. The ionic content of the active site directly affects the dissociation of ATP and products. Only one ion dissociates along with ATP in the two-Mg(2+) binding site, suggesting that the other ion binds EF prior to ATP association. Dissociation of reaction products cAMP and PPi is impaired by direct electrostatic interactions between products and Mg(2+) ions. This provides an explanation for the inhibitory effect of high Mg(2+) concentrations on EF enzymatic activity. Breaking of electrostatic interactions is dependent on a competitive binding of water molecules to the ions, and thus on the solvent accessibility of the active site. Consequently, product dissociation seems to be a two-step process. First, ligands are progressively solvated while preserving the most important electrostatic interactions, in a process that is dependent on the flexibility of the active site. Second, breakage of the electrostatic bonds follows, and ligands diffuse into solvent. In agreement with this mechanism, product protonation facilitates dissociation.
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Affiliation(s)
- Leandro Martínez
- Unité de Bioinformatique Structurale, URA CNRS 2185, Institut Pasteur, 25, rue du Dr Roux, F-75015 Paris, France.
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67
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Staiger N, Marx A. A DNA polymerase with increased reactivity for ribonucleotides and C5-modified deoxyribonucleotides. Chembiochem 2011; 11:1963-6. [PMID: 20734370 DOI: 10.1002/cbic.201000384] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Nadine Staiger
- Department of Chemistry, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany
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68
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69
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Kristiansen H, Gad HH, Eskildsen-Larsen S, Despres P, Hartmann R. The oligoadenylate synthetase family: an ancient protein family with multiple antiviral activities. J Interferon Cytokine Res 2010; 31:41-7. [PMID: 21142819 DOI: 10.1089/jir.2010.0107] [Citation(s) in RCA: 221] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The 2'-5' oligoadenylate synthetases (OAS) are interferon-induced antiviral enzymes that recognize virally produced dsRNA and initiate RNA destabilization through activation of RNase L within infected cells. However, recent evidence points toward several RNase L-independent pathways, through which members of the OAS family can exert antiviral activity. The crystal structure of OAS led to a novel insight into the catalytic mechanism, and revealed a remarkable similarity between OAS, Polyadenosine polymerase, and the class I CCA-adding enzyme from Archeoglobus fulgidus. This, combined with a variety of bioinformatic data, leads to the definition of a superfamily of template independent polymerases and proved that the OAS family are ancient proteins, which probably arose as early as the beginning of metazoan evolution.
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Affiliation(s)
- Helle Kristiansen
- Centre for Structural Biology, Department of Molecular Biology, Aarhus University, Aarhus, Denmark
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70
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Bermek O, Grindley NDF, Joyce CM. Distinct roles of the active-site Mg2+ ligands, Asp882 and Asp705, of DNA polymerase I (Klenow fragment) during the prechemistry conformational transitions. J Biol Chem 2010; 286:3755-66. [PMID: 21084297 DOI: 10.1074/jbc.m110.167593] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA polymerases catalyze the incorporation of deoxynucleoside triphosphates into a growing DNA chain using a pair of Mg(2+) ions, coordinated at the active site by two invariant aspartates, whose removal by mutation typically reduces the polymerase activity to barely detectable levels. Using two stopped-flow fluorescence assays that we developed previously, we have investigated the role of the carboxylate ligands, Asp(705) and Asp(882), of DNA polymerase I (Klenow fragment) in the early prechemistry steps that prepare the active site for catalysis. We find that neither carboxylate is required for an early conformational transition, reported by a 2-aminopurine probe, that takes place in the open ternary complex after binding of the complementary dNTP. However, the subsequent fingers-closing step requires Asp(882); this step converts the open ternary complex into the closed conformation, creating the active-site geometry required for catalysis. Crystal structures indicate that the Asp(882) position changes very little during fingers-closing; this side chain may therefore serve as an anchor point to receive the dNTP-associated metal ion as the nucleotide is delivered into the active site. The Asp(705) carboxylate is not required until after the fingers-closing step, and we suggest that its role is to facilitate the entry of the second Mg(2+) into the active site. The two early prechemistry steps that we have studied take place normally at very low Mg(2+) concentrations, although higher concentrations are needed for covalent nucleotide addition, consistent with the second metal ion entering the ternary complex after fingers-closing.
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Affiliation(s)
- Oya Bermek
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
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71
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Pupov DV, Kulbachinskiy AV. Structural dynamics of the active center of multisubunit RNA polymerases during RNA synthesis and proofreading. Mol Biol 2010. [DOI: 10.1134/s0026893310040023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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72
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Betat H, Rammelt C, Mörl M. tRNA nucleotidyltransferases: ancient catalysts with an unusual mechanism of polymerization. Cell Mol Life Sci 2010; 67:1447-63. [PMID: 20155482 PMCID: PMC11115931 DOI: 10.1007/s00018-010-0271-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 12/14/2009] [Accepted: 01/14/2010] [Indexed: 10/19/2022]
Abstract
RNA polymerases are important enzymes involved in the realization of the genetic information encoded in the genome. Thereby, DNA sequences are used as templates to synthesize all types of RNA. Besides these classical polymerases, there exists another group of RNA polymerizing enzymes that do not depend on nucleic acid templates. Among those, tRNA nucleotidyltransferases show remarkable and unique features. These enzymes add the nucleotide triplet C-C-A to the 3'-end of tRNAs at an astonishing fidelity and are described as "CCA-adding enzymes". During this incorporation of exactly three nucleotides, the enzymes have to switch from CTP to ATP specificity. How these tasks are fulfilled by rather simple and small enzymes without the help of a nucleic acid template is a fascinating research area. Surprising results of biochemical and structural studies allow scientists to understand at least some of the mechanistic principles of the unique polymerization mode of these highly unusual enzymes.
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Affiliation(s)
- Heike Betat
- Institute for Biochemistry, University of Leipzig, Brüderstr. 34, 04103 Leipzig, Germany
| | - Christiane Rammelt
- Institute for Biochemistry, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle, Germany
| | - Mario Mörl
- Institute for Biochemistry, University of Leipzig, Brüderstr. 34, 04103 Leipzig, Germany
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73
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Kilshtain AV, Warshel A. On the origin of the catalytic power of carboxypeptidase A and other metalloenzymes. Proteins 2010; 77:536-50. [PMID: 19480013 DOI: 10.1002/prot.22466] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Zinc metalloenzymes play a major role in key biological processes and carboxypeptidase-A (CPA) is a major prototype of such enzymes. The present work quantifies the energetics of the catalytic reaction of CPA and its mutants using the empirical valence bond (EVB) approach. The simulations allow us to quantify the origin of the catalytic power of this enzyme and to examine different mechanistic alternatives. The first step of the analysis used experimental information to determine the activation energy of each assumed mechanism of the reference reaction without the enzyme. The next step of the analysis involved EVB simulations of the reference reaction and then a calibration of the simulations by forcing them to reproduce the energetics of the reference reaction, in each assumed mechanism. The calibrated EVB was then used in systematic simulations of the catalytic reaction in the protein environment, without changing any parameter. The simulations reproduced the observed rate enhancement in two feasible general acid-general base mechanisms (GAGB-1 and GAGB-2), although the calculations with the GAGB-2 mechanism underestimated the catalytic effect in some treatments. We also reproduced the catalytic effect in the R127A mutant. The mutation calculations indicate that the GAGB-2 mechanism is significantly less likely than the GAGB-1 mechanism. It is also found, that the enzyme loses all its catalytic effect without the metal. This and earlier studies show that the catalytic effect of the metal is not some constant electrostatic effect, that can be assessed from gas phase studies, but a reflection of the dielectric effect of the specific environment.
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74
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Lansdon EB, Samuel D, Lagpacan L, Brendza KM, White KL, Hung M, Liu X, Boojamra CG, Mackman RL, Cihlar T, Ray AS, McGrath ME, Swaminathan S. Visualizing the molecular interactions of a nucleotide analog, GS-9148, with HIV-1 reverse transcriptase-DNA complex. J Mol Biol 2010; 397:967-78. [PMID: 20156454 DOI: 10.1016/j.jmb.2010.02.019] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Revised: 02/05/2010] [Accepted: 02/10/2010] [Indexed: 11/30/2022]
Abstract
GS-9148 ([5-(6-amino-purin-9-yl)-4-fluoro-2,5-dihydro-furan-2-yloxymethyl]-phosphonic acid) is a dAMP (2'-deoxyadenosine monophosphate) analog that maintains its antiviral activity against drug-resistant HIV. Crystal structures for HIV-1 reverse transcriptase (RT) bound to double-stranded DNA, ternary complexes with either GS-9148-diphosphate or 2'-deoxyadenosine triphosphate (dATP), and a post-incorporation structure with GS-9148 translocated to the priming site were obtained to gain insight into the mechanism of RT inhibition. The binding of either GS-9148-diphosphate or dATP to the binary RT-DNA complex resulted in the fingers subdomain closing around the incoming substrate. This produced up to a 9 A shift in the tips of the fingers subdomain as it closed toward the palm and thumb subdomains. GS-9148-diphosphate shows a similar binding mode as dATP in the nucleotide-binding site. Residues whose mutations confer resistance to nucleotide/nucleoside RT inhibitors, such as M184, Y115, L74, and K65, show little to no shift in orientation whether GS-9148-diphosphate or dATP is bound. One difference observed in binding is the position of the central ring. The dihydrofuran ring of GS-9148-diphosphate interacts with the aromatic side chain of Y115 more than does the ribose ring of dATP, possibly picking up a favorable pi-pi interaction. The ability of GS-9148-diphosphate to mimic the active-site contacts of dATP may explain its effective inhibition of RT and maintained activity against resistance mutations. Interestingly, the 2'-fluoro moiety of GS-9148-diphosphate was found in close proximity to the Q151 side chain, potentially explaining the observed moderately reduced susceptibly to GS-9148 conferred by Q151M mutation.
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Affiliation(s)
- Eric B Lansdon
- Gilead Sciences, Inc., 333 Lakeside Drive, Foster City, CA 94404, USA.
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75
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Menéndez-Arias L. Mutation rates and intrinsic fidelity of retroviral reverse transcriptases. Viruses 2009; 1:1137-65. [PMID: 21994586 PMCID: PMC3185545 DOI: 10.3390/v1031137] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Revised: 12/03/2009] [Accepted: 12/03/2009] [Indexed: 11/27/2022] Open
Abstract
Retroviruses are RNA viruses that replicate through a DNA intermediate, in a process catalyzed by the viral reverse transcriptase (RT). Although cellular polymerases and host factors contribute to retroviral mutagenesis, the RT errors play a major role in retroviral mutation. RT mutations that affect the accuracy of the viral polymerase have been identified by in vitro analysis of the fidelity of DNA synthesis, by using enzymological (gel-based) and genetic assays (e.g., M13mp2 lacZ forward mutation assays). For several amino acid substitutions, these observations have been confirmed in cell culture using viral vectors. This review provides an update on studies leading to the identification of the major components of the fidelity center in retroviral RTs.
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Affiliation(s)
- Luis Menéndez-Arias
- Centro de Biología Molecular "Severo Ochoa" [Consejo Superior de Investigaciones Científicas (CSIC) & Universidad Autónoma de Madrid], Campus de Cantoblanco, 28049 Madrid, Spain; E-Mail: ; Tel.: +34 91 196 4494
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76
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Nucleoside and nucleotide HIV reverse transcriptase inhibitors: 25 years after zidovudine. Antiviral Res 2009; 85:39-58. [PMID: 19887088 DOI: 10.1016/j.antiviral.2009.09.014] [Citation(s) in RCA: 261] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Revised: 09/19/2009] [Accepted: 09/23/2009] [Indexed: 12/29/2022]
Abstract
Twenty-five years ago, nucleoside analog 3'-azidothymidine (AZT) was shown to efficiently block the replication of HIV in cell culture. Subsequent studies demonstrated that AZT acts via the selective inhibition of HIV reverse transcriptase (RT) by its triphosphate metabolite. These discoveries have established the first class of antiretroviral agents: nucleoside and nucleotide reverse transcriptase inhibitors (NRTIs). Over the years that followed, NRTIs evolved into the main component of antiretroviral drug combinations that are now used for the treatment of all populations of HIV infected patients. A total of thirteen NRTI drug products are now available for clinical application: eight individual NRTIs, four fixed-dose combinations of two or three NRTIs, and one complete fixed-dose regimen containing two NRTIs and one non-nucleoside RT inhibitor. Multiple NRTIs or their prodrugs are in various stages of clinical development and new potent NRTIs are still being identified through drug discovery efforts. This article will review basic principles of the in vitro and in vivo pharmacology of NRTIs, discuss their clinical use including limitations associated with long-term NRTI therapy, and describe newly identified NRTIs with promising pharmacological profiles highlighting those in the development pipeline. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, volume 85, issue 1, 2010.
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77
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phi29 DNA polymerase active site: role of residue Val250 as metal-dNTP complex ligand and in protein-primed initiation. J Mol Biol 2009; 395:223-33. [PMID: 19883660 DOI: 10.1016/j.jmb.2009.10.061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 10/19/2009] [Accepted: 10/27/2009] [Indexed: 11/23/2022]
Abstract
DNA polymerases require two acidic residues to coordinate metal ions A and B at their polymerisation active site during catalysis of nucleotide incorporation. Crystallographic resolution of varphi29 DNA polymerase ternary complex showed that metal B coordination also depends on the carbonyl group of Val250 that belongs to the highly conserved Dx(2)SLYP motif of eukaryotic-type (family B) DNA polymerases. In addition, multiple sequence alignments have shown the specific conservation of this residue among the DNA polymerases that use a protein as primer. Thus, to ascertain its role in polymerisation, we have analysed the behaviour of single mutations introduced at the corresponding Val250 of varphi29 DNA polymerase. The differences in nucleotide binding affinity shown by mutants V250A and V250F with respect to the wild-type DNA polymerase agree to a role for Val250 as a metal B-dNTP complex ligand. In addition, mutant V250F was severely affected in varphi29 DNA replication because of a large reduction in the catalytic efficiency of the protein-primed reactions. In the light of the varphi29 DNA polymerase structures, a role for Val250 residue in the maintenance of the proper architecture of the enzyme to perform the protein-primed reactions is also proposed.
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78
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Beard WA, Shock DD, Batra VK, Pedersen LC, Wilson SH. DNA polymerase beta substrate specificity: side chain modulation of the "A-rule". J Biol Chem 2009; 284:31680-9. [PMID: 19759017 DOI: 10.1074/jbc.m109.029843] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apurinic/apyrimidinic (AP) sites are continuously generated in genomic DNA. Left unrepaired, AP sites represent noninstructional premutagenic lesions that are impediments to DNA synthesis. When DNA polymerases encounter an AP site, they generally insert dAMP. This preferential insertion is referred to as the A-rule. Crystallographic structures of DNA polymerase (pol) beta, a family X polymerase, with active site mismatched nascent base pairs indicate that the templating (i.e. coding) base is repositioned outside of the template binding pocket thereby diminishing interactions with the incorrect incoming nucleotide. This effectively produces an abasic site because the template pocket is devoid of an instructional base. However, the template pocket is not empty; an arginine residue (Arg-283) occupies the space vacated by the templating nucleotide. In this study, we analyze the kinetics of pol beta insertion opposite an AP site and show that the preferential incorporation of dAMP is lost with the R283A mutant. The crystallographic structures of pol beta bound to gapped DNA with an AP site analog (tertrahydrofuran) in the gap (binary complex) and with an incoming nonhydrolyzable dATP analog (ternary complex) were solved. These structures reveal that binding of the dATP analog induces a closed polymerase conformation, an unstable primer terminus, and an upstream shift of the templating residue even in the absence of a template base. Thus, dATP insertion opposite an abasic site and dATP misinsertions have common features.
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Affiliation(s)
- William A Beard
- Laboratory of Structural Biology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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79
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Lestienne PP. Are there three polynucleotide strands in the catalytic centre of DNA polymerases? Biochimie 2009; 91:1523-30. [PMID: 19628017 DOI: 10.1016/j.biochi.2009.07.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
Mitochondrial DNA may undergo large-scale rearrangements, thus leading to diseases. The mechanisms of these rearrangements are still the matter of debates. Several lines of evidence indicate that breakpoints are characterized by direct repeats (DR), one of them being eliminated from the normal genome. Analysis of DR showed their skewed nucleotide content compatible with the formation of known triple helices. Here, I propose a novel mechanism involving the formation of triplex structures that result from the dissociation of the [synthesized repeat-DNA polymerase] complex. Upon binding to the homologous sequence, replication is initiated from the primer bound in a triple helix manner. This feature implies the initiation of replication on the double-stranded DNA from the triple helix primer. Hereby, I review evidences supporting this model. Indeed, all short d(G)-rich primers 10 nucleotides long can be elongated on double-stranded DNA by phage, bacterial, reverse transcriptases and eukaryotic DNA polymerases. Mismatches may be tolerated between the primer and its double-stranded binding site. In contrast to previous studies, evidences for the parallel binding of the triple helix to its homologous strand are provided. This suggest the displacement of the non-template strand by the triple helix primer upon binding within the DNA polymerase catalytic centre. Computer modelling indicates that the triple helix primer lies within the major groove of the double helix, with its 3' hydroxyl end nearby the catalytic amino acids. Taken together, I bring new concepts on DNA rearrangements, and novel features of triple helices and DNA polymerases that can bind three polynucleotide strands similar to RNA polymerases.
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Affiliation(s)
- Patrick P Lestienne
- U 889 INSERM, Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux, France
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80
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Abstract
PAP (polyadenylate polymerase) is the template-independent RNA polymerase responsible for synthesis of the 3' poly(A) tails of mRNA. To investigate the role of proton transfer in the catalytic mechanism of PAP, the pH dependence of the steady-state kinetic parameters of yeast PAP were determined for the forward (adenyl transfer) and reverse (pyrophosphorolysis) reactions. The results indicate that productive formation of an enzyme-RNA-MgATP complex is pH independent over a broad pH range, but that formation of an active enzyme-RNA-MgPPi complex is strongly pH dependent, consistent with the production of a proton on the enzyme in the forward reaction. The pH dependence of the maximum velocity of the forward reaction suggests two protonic species are involved in enzyme catalysis. Optimal enzyme activity requires one species to be protonated and the other deprotonated. The deuterium solvent isotope effect on Vmax is also consistent with proton transfer involved in catalysis of a rate-determining step. Finally, pKa calculations of PAP were performed by the MCCE (multiconformational continuum electrostatic) method. Together, the data support that the protonation of residues Lys215 and Tyr224 exhibit co-operativity that is important for MgATP2- and MgPPi2- binding/dissociation, and suggest these residues function in electrostatic, but not in general acid, catalysis.
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81
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Bakhtina M, Roettger MP, Tsai MD. Contribution of the reverse rate of the conformational step to polymerase beta fidelity. Biochemistry 2009; 48:3197-208. [PMID: 19231836 DOI: 10.1021/bi802119f] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A complete understanding of the kinetic mechanism of fidelity requires comparison of correct and incorrect dNTP incorporation pathways in both the forward and reverse directions. The studies presented here focus on the dNTP-induced conformational step, which has historically been proposed by many to be the major determinant of fidelity. As it was recently highlighted [Tsai, Y. C., and Johnson, K. A. (2006) Biochemistry 45, 9675-9687], chemistry can be the slowest step in the forward direction of the correct dNTP incorporation pathway, yet the corresponding microscopic rate constant would not contribute toward fidelity in the case when the reverse rate of the conformational step is slower than chemistry. Here we use a stopped-flow technique to directly measure the reverse rate of the conformational step in the DNA polymerase beta (Pol beta) kinetic pathway. Extensive pre-steady-state kinetic studies presented include the utilization of 2-aminopurine-labeled DNA substrates, 2-aminopurine nucleotide triphosphate, a nonhydrolyzable nucleotide analogue dAMPCPP, and a rapid sequential mixing reaction scheme. Additionally, the effect of mismatched dNTPs, various metal ions, and the presence of the 3'-terminal hydroxyl group of the primer on the rate of the reverse "opening" conformational step were analyzed. Our analyses indicate that reverse "opening" is drastically facilitated in the presence of mismatched ternary complexes, which is in agreement with the hypothesis that the ternary complex is destabilized by the presence of incorrect dNTP. By analysis of the relative magnitudes of chemistry and reverse "opening" in the presence of both matched and mismatched matched ternary complexes, this work further validates that, for Pol beta, fidelity is dictated by the differences in free energy required to reach the highest energy transition state of the chemical step.
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Affiliation(s)
- Marina Bakhtina
- Department of Chemistry and The Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio 43210, USA
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82
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Insights into the replisome from the structure of a ternary complex of the DNA polymerase III alpha-subunit. J Mol Biol 2008; 382:859-69. [PMID: 18691598 PMCID: PMC2614274 DOI: 10.1016/j.jmb.2008.07.058] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2008] [Accepted: 07/22/2008] [Indexed: 01/07/2023]
Abstract
The crystal structure of the catalytic alpha-subunit of the DNA polymerase III (Pol IIIalpha) holoenzyme bound to primer-template DNA and an incoming deoxy-nucleoside 5'-triphosphate has been determined at 4.6-A resolution. The polymerase interacts with the sugar-phosphate backbone of the DNA across its minor groove, which is made possible by significant movements of the thumb, finger, and beta-binding domains relative to their orientations in the unliganded polymerase structure. Additionally, the DNA and incoming nucleotide are bound to the active site of Pol IIIalpha nearly identically as they are in their complex with DNA polymerase beta, thereby proving that the eubacterial replicating polymerase, but not the eukaryotic replicating polymerase, is homologous to DNA polymerase beta. Finally, superimposing a recent structure of the clamp bound to DNA on this Pol IIIalpha complex with DNA places a loop of the beta-binding domain into the appropriate clamp cleft and supports a mechanism of polymerase switching.
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83
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Sampoli Benítez BA, Arora K, Balistreri L, Schlick T. Mismatched base-pair simulations for ASFV Pol X/DNA complexes help interpret frequent G*G misincorporation. J Mol Biol 2008; 384:1086-97. [PMID: 18955064 DOI: 10.1016/j.jmb.2008.10.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 10/02/2008] [Accepted: 10/06/2008] [Indexed: 10/21/2022]
Abstract
DNA polymerase X (pol X) from the African swine fever virus is a 174-amino-acid repair polymerase that likely participates in a viral base excision repair mechanism, characterized by low fidelity. Surprisingly, pol X's insertion rate of the G*G mispair is comparable to that of the four Watson-Crick base pairs. This behavior is in contrast with another X-family polymerase, DNA polymerase beta (pol beta), which inserts G*G mismatches poorly, and has higher DNA repair fidelity. Using molecular dynamics simulations, we previously provided support for an induced-fit mechanism for pol X in the presence of the correct incoming nucleotide. Here, we perform molecular dynamics simulations of pol X/DNA complexes with different incoming incorrect nucleotides in various orientations [C*C, A*G, and G*G (anti) and A*G and G*G (syn)] and compare the results to available kinetic data and prior modeling. Intriguingly, the simulations reveal that the G*G mispair with the incoming nucleotide in the syn configuration undergoes large-scale conformational changes similar to that observed in the presence of correct base pair (G*C). The base pairing in the G*G mispair is achieved via Hoogsteen hydrogen bonding with an overall geometry that is well poised for catalysis. Simulations for other mismatched base pairs show that an intermediate closed state is achieved for the A*G and G*G mispair with the incoming dGTP in anti conformation, while the protein remains near the open conformation for the C*C and the A*G syn mismatches. In addition, catalytic site geometry and base pairing at the nascent template-incoming nucleotide interaction reveal distortions and misalignments that range from moderate for A*G anti to worst for the C*C complex. These results agree well with kinetic data for pol X and provide a structural/dynamic basis to explain, at atomic level, the fidelity of this polymerase compared with other members of the X family. In particular, the more open and pliant active site of pol X, compared to pol beta, allows pol X to accommodate bulkier mismatches such as guanine opposite guanine, while the more structured and organized pol beta active site imposes higher discrimination, which results in higher fidelity. The possibility of syn conformers resonates with other low-fidelity enzymes such as Dpo4 (from the Y family), which readily accommodate oxidative lesions.
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Affiliation(s)
- Benedetta A Sampoli Benítez
- Department of Natural Sciences and Mathematics, Marymount Manhattan College, 221 East 71st Street, New York, NY 10021, USA
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84
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Wang Y, Schlick T. Quantum mechanics/molecular mechanics investigation of the chemical reaction in Dpo4 reveals water-dependent pathways and requirements for active site reorganization. J Am Chem Soc 2008; 130:13240-50. [PMID: 18785738 PMCID: PMC3195406 DOI: 10.1021/ja802215c] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The nucleotidyl-transfer reaction coupled with the conformational transitions in DNA polymerases is critical for maintaining the fidelity and efficiency of DNA synthesis. We examine here the possible reaction pathways of a Y-family DNA polymerase, Sulfolobus solfataricus DNA polymerase IV (Dpo4), for the correct insertion of dCTP opposite 8-oxoguanine using the quantum mechanics/molecular mechanics (QM/MM) approach, both from a chemistry-competent state and a crystal closed state. The latter examination is important for understanding pre-chemistry barriers to interpret the entire enzyme mechanism, since the crystal closed state is not an ideal state for initiating the chemical reaction. The most favorable reaction path involves initial deprotonation of O3'H via two bridging water molecules to O1A, overcoming an overall potential energy barrier of approximately 20.0 kcal/mol. The proton on O1A-P(alpha) then migrates to the gamma-phosphate oxygen of the incoming nucleotide as O3' attacks P(alpha), and the P(alpha)-O3A bond breaks. The other possible pathway in which the O3'H proton is transferred directly to O1A on P(alpha) has an overall energy barrier of 25.0 kcal/mol. In both reaction paths, the rate-limiting step is the initial deprotonation, and the trigonal-bipyramidal configuration for P(alpha) occurs during the concerted bond formation (O3'-P(alpha)) and breaking (P(alpha)-O3A), indicating the associative nature of the chemical reaction. In contrast, the Dpo4/DNA complex with an imperfect active-site geometry corresponding to the crystal state must overcome a much higher activation energy barrier (29.0 kcal/mol) to achieve a tightly organized site due to hindered O3'H deprotonation stemming from larger distances and distorted conformation of the proton acceptors. This significant difference demonstrates that the pre-chemistry reorganization in Dpo4 costs approximately 4.0 to 9.0 kcal/mol depending on the primer terminus environment. Compared to the higher fidelity DNA polymerase beta from the X-family, Dpo4 has a higher chemical reaction barrier (20.0 vs 15.0 kcal/mol) due to the more solvent-exposed active site.
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Affiliation(s)
- Yanli Wang
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York University, New York, NY 10012
| | - Tamar Schlick
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York University, New York, NY 10012
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85
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Iyer LM, Abhiman S, Aravind L. A new family of polymerases related to superfamily A DNA polymerases and T7-like DNA-dependent RNA polymerases. Biol Direct 2008; 3:39. [PMID: 18834537 PMCID: PMC2579912 DOI: 10.1186/1745-6150-3-39] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 10/04/2008] [Indexed: 12/24/2022] Open
Abstract
Using sequence profile methods and structural comparisons we characterize a previously unknown family of nucleic acid polymerases in a group of mobile elements from genomes of diverse bacteria, an algal plastid and certain DNA viruses, including the recently reported Sputnik virus. Using contextual information from domain architectures and gene-neighborhoods we present evidence that they are likely to possess both primase and DNA polymerase activity, comparable to the previously reported prim-pol proteins. These newly identified polymerases help in defining the minimal functional core of superfamily A DNA polymerases and related RNA polymerases. Thus, they provide a framework to understand the emergence of both DNA and RNA polymerization activity in this class of enzymes. They also provide evidence that enigmatic DNA viruses, such as Sputnik, might have emerged from mobile elements coding these polymerases.
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Affiliation(s)
- Lakshminarayan M Iyer
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
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86
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Prato S, Vitale RM, Contursi P, Lipps G, Saviano M, Rossi M, Bartolucci S. Molecular modeling and functional characterization of the monomeric primase-polymerase domain from the Sulfolobus solfataricus plasmid pIT3. FEBS J 2008; 275:4389-402. [PMID: 18671730 DOI: 10.1111/j.1742-4658.2008.06585.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A tri-functional monomeric primase-polymerase domain encoded by the plasmid pIT3 from Sulfolobus solfataricus strain IT3 was identified using a structural-functional approach. The N-terminal domain of the pIT3 replication protein encompassing residues 31-245 (i.e. Rep245) was modeled onto the crystallographic structure of the bifunctional primase-polymerase domain of the archaeal plasmid pRN1 and refined by molecular dynamics in solution. The Rep245 protein was purified following overexpression in Escherichia coli and its nucleic acid synthesis activity was characterized. The biochemical properties of the polymerase activity such as pH, temperature optima and divalent cation metal dependence were described. Rep245 was capable of utilizing both ribonucleotides and deoxyribonucleotides for de novo primer synthesis and it synthesized DNA products up to several kb in length in a template-dependent manner. Interestingly, the Rep245 primase-polymerase domain harbors also a terminal nucleotidyl transferase activity, being able to elongate the 3'-end of synthetic oligonucleotides in a non-templated manner. Comparative sequence-structural analysis of the modeled Rep245 domain with other archaeal primase-polymerases revealed some distinctive features that could account for the multifaceted activities exhibited by this domain. To the best of our knowledge, Rep245 typifies the shortest functional domain from a crenarchaeal plasmid endowed with DNA and RNA synthesis and terminal transferase activity.
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Affiliation(s)
- Santina Prato
- Dipartimento di Biologia Strutturale e Funzionale, Università degli Studi di Napoli Federico II, Naples, Italy
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87
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Batra VK, Beard WA, Shock DD, Pedersen LC, Wilson SH. Structures of DNA polymerase beta with active-site mismatches suggest a transient abasic site intermediate during misincorporation. Mol Cell 2008; 30:315-24. [PMID: 18471977 DOI: 10.1016/j.molcel.2008.02.025] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Revised: 01/31/2008] [Accepted: 02/28/2008] [Indexed: 10/22/2022]
Abstract
We report the crystallographic structures of DNA polymerase beta with dG-dAMPCPP and dC-dAMPCPP mismatches in the active site. These premutagenic structures were obtained with a nonhydrolyzable incoming nucleotide analog, dAMPCPP, and Mn(2+). Substituting Mn(2+) for Mg(2+) significantly decreases the fidelity of DNA synthesis. The structures reveal that the enzyme is in a closed conformation like that observed with a matched Watson-Crick base pair. The incorrect dAMPCPP binds in a conformation identical to that observed with the correct nucleotide. To accommodate the incorrect nucleotide and closed protein conformation, the template strand in the vicinity of the active site has shifted upstream over 3 A, removing the coding base from the active site and generating an abasic templating pocket. The primer terminus rotates as its complementary template base is repositioned. This rotation moves O3' of the primer terminus away from the alpha-phosphate of the incoming nucleotide, thereby deterring misincorporation.
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Affiliation(s)
- Vinod K Batra
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC 27709, USA
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88
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Lestienne PP, Boudsocq F, Bonnet JE. Initiation of DNA replication by a third parallel DNA strand bound in a triple-helix manner leads to strand invasion. Biochemistry 2008; 47:5689-98. [PMID: 18454553 DOI: 10.1021/bi702318g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
According to current knowledge, DNA polymerases accommodate only two polynucleotide strands in their catalytic site: the template and the primer to be elongated. Here we show that in addition to these two polynucleotide strands, HIV-1 and AMV reverse transcriptases, human DNA polymerases beta, gamma, and lambda, and the archaebacterial Dpo4 can elongate 10-nucleotide primers bound in a triple-helix manner to hairpin duplex DNA tethered by a few thymidine residues. The elongation occurs when the primer is parallel to the homologous strand. This feature was confirmed by using complementary single-stranded DNA with restricted nucleotide composition which bound polypurine and polypyrimidine primers at an asymmetric site. The results unambiguously confirmed the previous experiments, showing binding of the primer strand parallel to the homologous sequence. The common feature of these DNA polymerases is that they all elongated dG-rich primers, whereas they behaved differently when other polynucleotide sequences were used. Interestingly, only five to seven dG residues at similar positions between the primer and its binding site can allow elongation, which may even be facilitated by a single C/C mismatch. We suggest that DNA polymerases displace the primer form Hoogsteen bonds to from Watson-Crick pairings, enabling subsequent priming of replication. These experiments indicate that DNA polymerases may bind three DNA strands, as RNA polymerases do, and provide a molecular basis for 3'-OH invasion at short similar sequences in the DNA double helix, yielding potential DNA rearrangements upon single-strand breakage.
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Affiliation(s)
- Patrick P Lestienne
- Université Victor Segalen Bordeaux 2, Laboratoire de Pharmacologie des Agents Anticancéreux, EAD 515, Institut Bergonié, F-33076 Bordeaux, France.
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89
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Mendieta J, Cases-González CE, Matamoros T, Ramírez G, Menéndez-Arias L. A Mg2+-induced conformational switch rendering a competent DNA polymerase catalytic complex. Proteins 2008; 71:565-74. [PMID: 17963236 DOI: 10.1002/prot.21711] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The structural and dynamical changes occurring before nucleotide addition were studied using molecular dynamics (MD) simulations of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) complexes containing one or two Mg2+ ions in the presence of dNTP. Our models revealed that the formation of a catalytically competent DNA polymerase complex required subtle rearrangements at the catalytic site A, which occurred only when an Mg2+ ion was bound. This model has been validated using pre-steady-state kinetics to show that free Mg2+ is necessary to obtain a catalytically competent polymerase. Kinetic studies carried out with Be2+ as a cofactor permitted the functional discrimination between metal sites A and B. At low concentrations, Be2+ increased the catalytic efficiency of the polymerase, while at higher concentrations, it competed with Mg2+ for binding to site A, and inhibited DNA polymerization. In agreement with experimental data, MD simulations revealed that the catalytic attack distance between the 3-OH of the primer and the phosphorus in complexes containing Be2+ instead of Mg2+ at site A was above 4.5 A. Our findings provide a detailed description of the mechanism of DNA polymerization and should be helpful to understand the molecular basis of DNA replication fidelity.
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Affiliation(s)
- Jesús Mendieta
- Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Cantoblanco, Madrid 28049, Spain
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90
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Pursell ZF, Kunkel TA. DNA polymerase epsilon: a polymerase of unusual size (and complexity). PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2008; 82:101-45. [PMID: 18929140 PMCID: PMC3694787 DOI: 10.1016/s0079-6603(08)00004-4] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zachary F. Pursell
- Laboratory of Molecular Genetics and Laboratory of Structural Biology National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709
| | - Thomas A. Kunkel
- Laboratory of Molecular Genetics and Laboratory of Structural Biology National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709
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91
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Tang KH, Niebuhr M, Aulabaugh A, Tsai MD. Solution structures of 2 : 1 and 1 : 1 DNA polymerase-DNA complexes probed by ultracentrifugation and small-angle X-ray scattering. Nucleic Acids Res 2007; 36:849-60. [PMID: 18084022 PMCID: PMC2241917 DOI: 10.1093/nar/gkm1101] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We report small-angle X-ray scattering (SAXS) and sedimentation velocity (SV) studies on the enzyme-DNA complexes of rat DNA polymerase beta (Pol beta) and African swine fever virus DNA polymerase X (ASFV Pol X) with one-nucleotide gapped DNA. The results indicated formation of a 2 : 1 Pol beta-DNA complex, whereas only 1 : 1 Pol X-DNA complex was observed. Three-dimensional structural models for the 2 : 1 Pol beta-DNA and 1 : 1 Pol X-DNA complexes were generated from the SAXS experimental data to correlate with the functions of the DNA polymerases. The former indicates interactions of the 8 kDa 5'-dRP lyase domain of the second Pol beta molecule with the active site of the 1 : 1 Pol beta-DNA complex, while the latter demonstrates how ASFV Pol X binds DNA in the absence of DNA-binding motif(s). As ASFV Pol X has no 5'-dRP lyase domain, it is reasonable not to form a 2 : 1 complex. Based on the enhanced activities of the 2 : 1 complex and the observation that the 8 kDa domain is not in an optimal configuration for the 5'-dRP lyase reaction in the crystal structures of the closed ternary enzyme-DNA-dNTP complexes, we propose that the asymmetric 2 : 1 Pol beta-DNA complex enhances the function of Pol beta.
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Affiliation(s)
- Kuo-Hsiang Tang
- Department of Chemistry, the Ohio State University, Columbus, OH 43210, USA
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92
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Benner S, Chen RJA, Wilson NA, Abu-Shumays R, Hurt N, Lieberman KR, Deamer DW, Dunbar WB, Akeson M. Sequence-specific detection of individual DNA polymerase complexes in real time using a nanopore. NATURE NANOTECHNOLOGY 2007; 2:718-24. [PMID: 18654412 PMCID: PMC2507869 DOI: 10.1038/nnano.2007.344] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2007] [Accepted: 09/19/2007] [Indexed: 05/20/2023]
Abstract
Nanoscale pores have potential to be used as biosensors and are an established tool for analysing the structure and composition of single DNA or RNA molecules. Recently, nanopores have been used to measure the binding of enzymes to their DNA substrates. In this technique, a polynucleotide bound to an enzyme is drawn into the nanopore by an applied voltage. The force exerted on the charged backbone of the polynucleotide by the electric field is used to examine the enzyme-polynucleotide interactions. Here we show that a nanopore sensor can accurately identify DNA templates bound in the catalytic site of individual DNA polymerase molecules. Discrimination among unbound DNA, binary DNA/polymerase complexes, and ternary DNA/polymerase/deoxynucleotide triphosphate complexes was achieved in real time using finite state machine logic. This technique is applicable to numerous enzymes that bind or modify DNA or RNA including exonucleases, kinases and other polymerases.
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93
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Knorre DG, Kudryashova NV, Lavrik OI. Chemical approaches to the elucidation of template biosynthesis: study of replication and reverse transcription. RUSSIAN CHEMICAL REVIEWS 2007. [DOI: 10.1070/rc1998v067n05abeh000420] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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94
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Bojin MD, Schlick T. A quantum mechanical investigation of possible mechanisms for the nucleotidyl transfer reaction catalyzed by DNA polymerase beta. J Phys Chem B 2007; 111:11244-52. [PMID: 17764165 DOI: 10.1021/jp071838c] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Several quantum mechanical (QM) and hybrid quantum/molecular mechanical (QM/MM) studies have been employed recently to analyze the nucleotidyl transfer reaction in DNA polymerase beta (pol beta). Our examination reveals strong dependence of the reported mechanism on the initial molecular model. Thus, we explore here several model systems by QM methods to investigate pol beta's possible pathway variations. Although our most favorable pathway involves a direct proton transfer from O3'(primer) to O2alpha(Palpha), we also discuss other initial proton-transfer steps--to an adjacent water, to triphosphate, or to aspartic units--and the stabilizing effect of crystallographic water molecules in the active site. Our favored reaction route has an energetically undemanding initial step of less than 1.0 kcal/mol (at the B3LYP/6-31G(d,p) level), and involves a slight rearrangement in the geometry of the active site. This is followed by two major steps: (1) direct proton transfer from O3'(primer) to O2alpha(Palpha) leading to the formation of a pentavalent, trigonal bipyramidal Palpha center, via an associative mechanism, at a cost of about 28 kcal/mol, and (2) breakage of the triphosphate unit (exothermic process, approximately 22 kcal/mol) that results in the full transfer of the nucleotide to the DNA and the formation of pyrophosphate. These energy values are expected to be lower in the physical system when full protein effects are incorporated. We also discuss variations from this dominant pathway, and their impact on the overall repair process. Our calculated barrier for the chemical reaction clearly indicates that chemistry is rate-limiting overall for correct nucleotide insertion in pol beta, in accord with other studies. Protonation studies on relevant intermediates suggest that, although protonation at a single aspartic residue may occur, the addition of a second proton to the system significantly disturbs the active site. We conclude that the active site rearrangement step necessary to attain a reaction-competent geometry is essential and closely related to the "pre-chemistry" avenue described recently as a key step in the overall kinetic cycle of DNA polymerases. Thus, our work emphasizes the many possible ways for DNA polymerase beta's chemical reaction to occur, determined by the active site environment and initial models.
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Affiliation(s)
- Mihaela D Bojin
- Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, New York 10012, USA
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95
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Alberts IL, Wang Y, Schlick T. DNA polymerase beta catalysis: are different mechanisms possible? J Am Chem Soc 2007; 129:11100-10. [PMID: 17696533 DOI: 10.1021/ja071533b] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DNA polymerases are crucial constituents of the complex cellular machinery for replicating and repairing DNA. Discerning mechanistic pathways of DNA polymerase on the atomic level is important for revealing the origin of fidelity discrimination. Mammalian DNA polymerase beta (pol beta), a small (39 kDa) member of the X-family, represents an excellent model system to investigate polymerase mechanisms. Here, we explore several feasible low-energy pathways of the nucleotide transfer reaction of pol beta for correct (according to Watson-Crick hydrogen bonding) G:C basepairing versus the incorrect G:G case within a consistent theoretical framework. We use mixed quantum mechanics/molecular mechanics (QM/MM) techniques in a constrained energy minimization protocol to effectively model not only the reactive core but also the influence of the rest of the enzymatic environment and explicit solvent on the reaction. The postulated pathways involve initial proton abstraction from the terminal DNA primer O3'H group, nucleophilic attack that extends the DNA primer chain, and elimination of pyrophosphate. In particular, we analyze several possible routes for the initial deprotonation step: (i) direct transfer to a phosphate oxygen O(Palpha) of the incoming nucleotide, (ii) direct transfer to an active site Asp group, and (iii) transfer to explicit water molecules. We find that the most probable initial step corresponds to step (iii), involving initial deprotonation to water, which is followed by proton migration to active site Asp residues, and finally to the leaving pyrophosphate group, with an activation energy of about 15 kcal/mol. We argue that initial deprotonation steps (i) and (ii) are less likely as they are at least 7 and 11 kcal/mol, respectively, higher in energy. Overall, the rate-determining step for both the correct and the incorrect nucleotide cases is the initial deprotonation in concert with nucleophilic attack at the phosphate center; however, the activation energy we obtain for the mismatched G:G case is 5 kcal/mol higher than that of the matched G:C complex, due to active site structural distortions. Taken together, our results support other reported mechanisms and help define a framework for interpreting nucleotide specificity differences across polymerase families, in terms of the concept of active site preorganization or the so-called "pre-chemistry avenue".
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Affiliation(s)
- Ian L Alberts
- Department of Chemistry and Courant Institute of Mathematical Sciences, 251 Mercer Street, New York University, New York, New York 10012, USA
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96
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Moon AF, Garcia-Diaz M, Batra VK, Beard WA, Bebenek K, Kunkel TA, Wilson SH, Pedersen LC. The X family portrait: structural insights into biological functions of X family polymerases. DNA Repair (Amst) 2007; 6:1709-25. [PMID: 17631059 PMCID: PMC2128704 DOI: 10.1016/j.dnarep.2007.05.009] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Accepted: 05/22/2007] [Indexed: 11/19/2022]
Abstract
The mammalian family X DNA polymerases (DNA polymerases beta, lambda, mu, and TdT) contribute to base excision repair and double-strand break repair by virtue of their ability to fill short gaps in DNA. Structural information now exists for all four of these enzymes, making this the first mammalian polymerase family whose structural portrait is complete. Here we consider how distinctive structural features of these enzymes contribute to their biological functions in vivo.
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Affiliation(s)
- Andrea F. Moon
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Miguel Garcia-Diaz
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Vinod K. Batra
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - William A. Beard
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Katarzyna Bebenek
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Thomas A. Kunkel
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Samuel H. Wilson
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
| | - Lars C. Pedersen
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences. 111 T.W. Alexander Drive, MD F3-09, Research Triangle Park, North Carolina 27709
- *Corresponding author: Phone: 919-541-0444; Fax: 919-541-7880;
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97
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Radhakrishnan R. Coupling of fast and slow modes in the reaction pathway of the minimal hammerhead ribozyme cleavage. Biophys J 2007; 93:2391-9. [PMID: 17545240 PMCID: PMC1965431 DOI: 10.1529/biophysj.107.104661] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
By employing classical molecular dynamics, correlation analysis of coupling between slow and fast dynamical modes, and free energy (umbrella) sampling using classical as well as mixed quantum mechanics molecular mechanics force fields, we uncover a possible pathway for phosphoryl transfer in the self-cleaving reaction of the minimal hammerhead ribozyme. The significance of this pathway is that it initiates from the minimal hammerhead crystal structure and describes the reaction landscape as a conformational rearrangement followed by a covalent transformation. The delineated mechanism is catalyzed by two metal (Mg(2+)) ions, proceeds via an in-line-attack by CYT 17 O2' on the scissile phosphorous (ADE 1.1 P), and is therefore consistent with the experimentally observed inversion configuration. According to the delineated mechanism, the coupling between slow modes involving the hammerhead backbone with fast modes in the cleavage site appears to be crucial for setting up the in-line nucleophilic attack.
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Affiliation(s)
- Ravi Radhakrishnan
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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98
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Liu Y, Purvis J, Shih A, Weinstein J, Agrawal N, Radhakrishnan R. A multiscale computational approach to dissect early events in the Erb family receptor mediated activation, differential signaling, and relevance to oncogenic transformations. Ann Biomed Eng 2007; 35:1012-25. [PMID: 17273938 PMCID: PMC3021414 DOI: 10.1007/s10439-006-9251-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2006] [Accepted: 12/12/2006] [Indexed: 11/24/2022]
Abstract
We describe a hierarchical multiscale computational approach based on molecular dynamics simulations, free energy-based molecular docking simulations, deterministic network-based kinetic modeling, and hybrid discrete/continuum stochastic dynamics protocols to study the dimer-mediated receptor activation characteristics of the Erb family receptors, specifically the epidermal growth factor receptor (EGFR). Through these modeling approaches, we are able to extend the prior modeling of EGF-mediated signal transduction by considering specific EGFR tyrosine kinase (EGFRTK) docking interactions mediated by differential binding and phosphorylation of different C-terminal peptide tyrosines on the RTK tail. By modeling signal flows through branching pathways of the EGFRTK resolved on a molecular basis, we are able to transcribe the effects of molecular alterations in the receptor (e.g., mutant forms of the receptor) to differing kinetic behavior and downstream signaling response. Our molecular dynamics simulations show that the drug sensitizing mutation (L834R) of EGFR stabilizes the active conformation to make the system constitutively active. Docking simulations show preferential characteristics (for wildtype vs. mutant receptors) in inhibitor binding as well as preferential enhancement of phosphorylation of particular substrate tyrosines over others. We find that in comparison to the wildtype system, the L834R mutant RTK preferentially binds the inhibitor erlotinib, as well as preferentially phosphorylates the substrate tyrosine Y1068 but not Y1173. We predict that these molecular level changes result in preferential activation of the Akt signaling pathway in comparison to the Erk signaling pathway for cells with normal EGFR expression. For cells with EGFR over expression, the mutant over activates both Erk and Akt pathways, in comparison to wildtype. These results are consistent with qualitative experimental measurements reported in the literature. We discuss these consequences in light of how the network topology and signaling characteristics of altered (mutant) cell lines are shaped differently in relationship to native cell lines.
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Affiliation(s)
- Yingting Liu
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd Street, Philadelphia, PA 19104, USA
| | - Jeremy Purvis
- Genomics and Computational Biology Program, University of Pennsylvania, Philadelphia, PA, USA
| | - Andrew Shih
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd Street, Philadelphia, PA 19104, USA
| | - Joshua Weinstein
- Department of Bioengineering, Stanford University, Stanford, CA, USA
| | - Neeraj Agrawal
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Ravi Radhakrishnan
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd Street, Philadelphia, PA 19104, USA
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA, USA
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA, USA
- Genomics and Computational Biology Program, University of Pennsylvania, Philadelphia, PA, USA
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99
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Castro C, Smidansky E, Maksimchuk KR, Arnold JJ, Korneeva VS, Götte M, Konigsberg W, Cameron CE. Two proton transfers in the transition state for nucleotidyl transfer catalyzed by RNA- and DNA-dependent RNA and DNA polymerases. Proc Natl Acad Sci U S A 2007; 104:4267-72. [PMID: 17360513 PMCID: PMC1838591 DOI: 10.1073/pnas.0608952104] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The rate-limiting step for nucleotide incorporation in the pre-steady state for most nucleic acid polymerases is thought to be a conformational change. As a result, very little information is available on the role of active-site residues in the chemistry of nucleotidyl transfer. For the poliovirus RNA-dependent RNA polymerase (3D(pol)), chemistry is partially (Mg(2+)) or completely (Mn(2+)) rate limiting. Here we show that nucleotidyl transfer depends on two ionizable groups with pK(a) values of 7.0 or 8.2 and 10.5, depending upon the divalent cation used in the reaction. A solvent deuterium isotope effect of three to seven was observed on the rate constant for nucleotide incorporation in the pre-steady state; none was observed in the steady state. Proton-inventory experiments were consistent with two protons being transferred during the rate-limiting transition state of the reaction, suggesting that both deprotonation of the 3'-hydroxyl nucleophile and protonation of the pyrophosphate leaving group occur in the transition state for phosphodiester bond formation. Importantly, two proton transfers occur in the transition state for nucleotidyl-transfer reactions catalyzed by RB69 DNA-dependent DNA polymerase, T7 DNA-dependent RNA polymerase and HIV reverse transcriptase. Interpretation of these data in the context of known polymerase structures suggests the existence of a general base for deprotonation of the 3'-OH nucleophile, although use of a water molecule cannot be ruled out conclusively, and a general acid for protonation of the pyrophosphate leaving group in all nucleic acid polymerases. These data imply an associative-like transition-state structure.
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Affiliation(s)
- Christian Castro
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
| | - Eric Smidansky
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
| | - Kenneth R. Maksimchuk
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
| | - Jamie J. Arnold
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
| | - Victoria S. Korneeva
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
| | - Matthias Götte
- Department of Microbiology and Immunology, McGill University, Montreal, QB, Canada H3A 2B4; and
| | - William Konigsberg
- Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, New Haven, CT 06520
| | - Craig E. Cameron
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, 201 Althouse Laboratory, University Park, PA 16802
- To whom correspondence should be addressed. E-mail:
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100
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Drosopoulos WC, Prasad VR. The active site residue Valine 867 in human telomerase reverse transcriptase influences nucleotide incorporation and fidelity. Nucleic Acids Res 2007; 35:1155-68. [PMID: 17264120 PMCID: PMC1851649 DOI: 10.1093/nar/gkm002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2006] [Revised: 12/22/2006] [Accepted: 12/22/2006] [Indexed: 11/14/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT), the catalytic subunit of human telomerase, contains conserved motifs common to retroviral reverse transcriptases and telomerases. Within the C motif of hTERT is the Leu866-Val867-Asp868-Asp869 tetrapeptide that includes a catalytically essential aspartate dyad. Site-directed mutagenesis of Tyr183 and Met184 residues in HIV-1 RT, residues analogous to Leu866 and Val867, revealed that they are key determinants of nucleotide binding, processivity and fidelity. In this study, we show that substitutions at Val867 lead to significant changes in overall enzyme activity and telomere repeat extension rate, but have little effect on polymerase processivity. All Val867 substitutions examined (Ala, Met, Thr) led to reduced repeat extension rates, ranging from approximately 20 to 50% of the wild-type rate. Reconstitution of V867M hTERT and telomerase RNAs (TRs) with mutated template sequences revealed the effect on extension rate was associated with a template copying defect specific to template A residues. Furthermore, the Val867 hTERT mutants also displayed increased nucleotide incorporation fidelity, implicating Val867 as a determinant of telomerase fidelity. These findings suggest that by evolving to have a valine at position 867, the wild-type hTERT protein may have partially compromised polymerase fidelity for optimal and rapid repeat synthesis.
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Affiliation(s)
- William C Drosopoulos
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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