101
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Matsuo H, Moriguchi T, Takagi T, Kusakabe T, Buratowski S, Sekine M, Kyogoku Y, Wagner G. Efficient Synthesis of 13C,15N-Labeled RNA Containing the Cap Structure m7GpppA. J Am Chem Soc 2000. [DOI: 10.1021/ja9926820] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hiroshi Matsuo
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Tomohisa Moriguchi
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Toshimitsu Takagi
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Takahiro Kusakabe
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Stephen Buratowski
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Mitsuo Sekine
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Yoshimasa Kyogoku
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
| | - Gerhard Wagner
- Contribution from the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, and Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
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102
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Abstract
Crystal structures have recently become available for two proteins (VP39 and eIF4E) complexed with their cognate ligand - the mRNA cap. Despite their total structural dissimilarity, both proteins bind N7-methylguanine between two parallel aromatic sidechains. The resulting stacked arrangement governs their high specificity for the alkylated form of the nucleobase.
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Affiliation(s)
- F A Quiocho
- Department of Biochemistry and the Structural and Computational Biology, Howard Hughes Medical Institute, Molecular Biophysics Graduate Program, Baylor College of Medicine, Houston, TX 77030, USA.
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103
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Wang H, Boisvert D, Kim KK, Kim R, Kim SH. Crystal structure of a fibrillarin homologue from Methanococcus jannaschii, a hyperthermophile, at 1.6 A resolution. EMBO J 2000; 19:317-23. [PMID: 10654930 PMCID: PMC305568 DOI: 10.1093/emboj/19.3.317] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Fibrillarin is a phylogenetically conserved protein essential for efficient processing of pre-rRNA through its association with a class of small nucleolar RNAs during ribosomal biogenesis. The protein is the antigen for the autoimmune disease scleroderma. Here we report the crystal structure of the fibrillarin homologue from Methanococcus jannaschii, a hyperthermophile, at 1.6 A resolution. The structure consists of two domains, with a novel fold in the N-terminal region and a methyltransferase-like domain in the C-terminal region. Mapping temperature-sensitive mutations found in yeast fibrillarin Nop1 to the Methanococcus homologue structure reveals that many of the mutations cluster in the core of the methyltransferase-like domain.
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Affiliation(s)
- H Wang
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
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104
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Abstract
This chapter focuses on the history of the discovery of cap and an update of research on viral and cellular-messenger RNA (mRNA) capping. Cap structures of the type m7 GpppN(m)pN(m)p are present at the 5′ ends of nearly all eukaryotic cellular and viral mRNAs. A cap is added to cellular mRNA precursors and to the transcripts of viruses that replicate in the nucleus during the initial phases of transcription and before other processing events, including internal N6A methylation, 3′-poly (A) addition, and exon splicing. Despite the variations on the methylation theme, the important biological consequences of a cap structure appear to correlate with the N7-methyl on the 5′-terminal G and the two pyrophosphoryl bonds that connect m7G in a 5′–5′ configuration to the first nucleotide of mRNA. In addition to elucidating the biochemical mechanisms of capping and the downstream effects of this 5′- modification on gene expression, the advent of gene cloning has made available an ever-increasing amount of information on the proteins responsible for producing caps and the functional effects of other cap-related interactions. Genetic approaches have demonstrated the lethal consequences of cap failure in yeasts, and complementation studies have shown the evolutionary functional conservation of capping from unicellular to metazoan organisms.
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Affiliation(s)
- Y Furuichi
- AGENE Research Institute, Kamakura, Japan
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105
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Johnson L, Gershon PD. RNA binding characteristics and overall topology of the vaccinia poly(A) polymerase-processivity factor-primer complex. Nucleic Acids Res 1999; 27:2708-21. [PMID: 10373588 PMCID: PMC148480 DOI: 10.1093/nar/27.13.2708] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The vaccinia virus-encoded heterodimer responsible for poly(A) tail elongation comprises a polyadenylylation catalytic subunit (VP55) and associated processivity factor (VP39). We show that monomeric VP39's affinity for RNA homopolymers follows the hierarchy poly(I) >poly(U) >>poly(G) >poly(A) >poly(C), that the heterodimer interacts stably with 40-45 nucleotide nucleic acid segments, and that its homopolymer preference for polyadenylylation priming is comparable to the VP39 affinity hierarchy (above). For oligonucleotide ligands possessing the previously-identified (rU)2-(N)25-rU heterodimer-binding motif, the heterodimer's affinity and base-type preference are mediated via both the (rU)2and rU portions, with the greater contribution coming from (rU)2. VP39's R107 sidechain contributes to specificity at the downstream rU. Substitution of each ribouridylate of the motif with either ribothymidine or 4-thiodeoxythymidine indicated that the downstream rU interacts with both heterodimer subunits, whereas the upstream (rU)2interacts only with VP55. A 'crosslinking SELEX' approach indicated VP39-base proximity around position -10 of a 4-thioribouridine/deoxycytidine ligand pool. Upon incubating the heterodimer with a panel of identical-sequence oligonucleotides derivatized with azidophenacyl bromide at various phosphate positions, those derivatized at positions -11 to -21 photocrosslinked to both subunits in a coordinated manner. This region may therefore pass through a 'cleft' or enclosed 'channel' at the subunit interface.
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Affiliation(s)
- L Johnson
- Department of Medical Biochemistry and Genetics/Institute of Biosciences and Technology, Texas A&M University, Houston, TX 77030, USA
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106
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Hu G, Gershon PD, Hodel AE, Quiocho FA. mRNA cap recognition: dominant role of enhanced stacking interactions between methylated bases and protein aromatic side chains. Proc Natl Acad Sci U S A 1999; 96:7149-54. [PMID: 10377383 PMCID: PMC22034 DOI: 10.1073/pnas.96.13.7149] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have determined, by high resolution x-ray analysis, 10 structures comprising the mRNA cap-specific methyltransferase VP39 or specific mutants thereof in the presence of methylated nucleobase analogs (N1-methyladenine, N3-methyladenine, N1-methylcytosine, N3-methylcytosine) and their unmethylated counterparts, or nucleoside N7-methylguanosine. Together with solution affinity studies and previous crystallographic data for N7-methylguanosine and its phosphorylated derivatives, these data demonstrate that only methylated, positively charged bases are bound, indicating that their enhanced stacking with two aromatic side chains of VP39 (Tyr 22 and Phe 180) plays a dominant role in cap recognition. Four key features characterize this stacking interaction: (i) near perfect parallel alignment between the sandwiched methylated bases and aromatic side chains, (ii) substantial areas of overlap in the two-stacked rings, (iii) a 3.4-A interplanar spacing within the overlapping region, and (iv) positive charge in the heterocyclic nucleobase.
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Affiliation(s)
- G Hu
- Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
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107
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Baber JL, Libutti D, Levens D, Tjandra N. High precision solution structure of the C-terminal KH domain of heterogeneous nuclear ribonucleoprotein K, a c-myc transcription factor. J Mol Biol 1999; 289:949-62. [PMID: 10369774 DOI: 10.1006/jmbi.1999.2818] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Among it's many reported functions, heterogeneous nuclear ribonucleoprotein (hnRNP) K is a transcription factor for the c- myc gene, a proto-oncogene critical for the regulation of cell growth and differentiation. We have determined the solution structure of the Gly26-->Arg mutant of the C-terminal K-homology (KH) domain of hnRNP K by NMR spectroscopy. This is the first structure investigation of hnRNP K. Backbone residual dipolar couplings, which provide information that is fundamentally different from the standard NOE-derived distance restraints, were employed to improve structure quality. An independent assessment of structure quality was achieved by comparing the backbone15N T1/T2ratios to the calculated structures. The C-terminal KH module of hnRNP K (KH3) is revealed to be a three-stranded beta-sheet stacked against three alpha-helices, two of which are nearly parallel to the strands of the beta-sheet. The Gly26-->Arg mutation abolishes single-stranded DNA binding without altering the overall fold of the protein. This provides a clue to possible nucleotide binding sites of KH3. It appears unlikely that the solvent-exposed side of the beta-sheet will be the site of protein-nucleic acid complex formation. This is in contrast to the earlier theme for protein-RNA complexes incorporating proteins structurally similar to KH3. We propose that the surface of KH3 that interacts with nucleic acid is comparable to the region of DNA interaction for the double-stranded DNA-binding domain of bovine papillomavirus-1 E2 that has a three-dimensional fold similar to that of KH3.
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Affiliation(s)
- J L Baber
- National Heart, Lung, and Blood Institute, National Institutes of Health, Building 3, Bethesda, MD, 20892-0380, USA
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108
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Schluckebier G, Zhong P, Stewart KD, Kavanaugh TJ, Abad-Zapatero C. The 2.2 A structure of the rRNA methyltransferase ErmC' and its complexes with cofactor and cofactor analogs: implications for the reaction mechanism. J Mol Biol 1999; 289:277-91. [PMID: 10366505 DOI: 10.1006/jmbi.1999.2788] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The rRNA methyltransferase ErmC' transfers methyl groups from S -adenosyl-l-methionine to atom N6 of an adenine base within the peptidyltransferase loop of 23 S rRNA, thus conferring antibiotic resistance against a number of macrolide antibiotics. The crystal structures of ErmC' and of its complexes with the cofactor S -adenosyl-l-methionine, the reaction product S-adenosyl-l-homocysteine and the methyltransferase inhibitor Sinefungin, respectively, show that the enzyme undergoes small conformational changes upon ligand binding. Overall, the ligand molecules bind to the protein in a similar mode as observed for other methyltransferases. Small differences between the binding of the amino acid parts of the different ligands are correlated with differences in their chemical structure. A model for the transition-state based on the atomic details of the active site is consistent with a one-step methyl-transfer mechanism and might serve as a first step towards the design of potent Erm inhibitors.
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Affiliation(s)
- G Schluckebier
- Abbott Laboratories, D46Y-AP 10, 100 Abbott Park Road, Abbott Park, IL, 60064, USA.
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109
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Deng L, Johnson L, Neveu JM, Hardin S, Wang SM, Lane WS, Gershon PD. A polyadenylylation-specific RNA-contact site on the surface of the bifunctional vaccinia virus RNA modifying protein VP39 that is distinct from the mRNA 5' end-binding "cleft". J Mol Biol 1999; 285:1417-27. [PMID: 9917386 DOI: 10.1006/jmbi.1998.2417] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
VP39 is a bifunctional mRNA-modifying protein that acts as both an mRNA cap-specific 2'-O-methyltransferase and a processivity factor for VP55, the vaccinia poly(A) polymerase catalytic subunit. Although regions of the protein surface required for methyltransferase function are well defined, it has been unclear whether the protein polyadenylylation function requires direct RNA contact and, if so, where the contact site(s) might be located on the protein surface. Here, we show that the VP55-VP39 heterodimer forms a stable complex with a 50mer oligonucleotide bearing a U2-N25-U motif, as opposed to the U2-N15-U motif that is optimal for stable complex formation with VP55 alone. An oligonucleotide bearing a U2-N25-U motif in which the downstream U residue is replaced with 4thioU can be efficiently photocrosslinked to VP39, but only in the context of the VP55-VP39 heterodimer. By partial proteolysis of end-labeled VP39, the site of oligonucleotide photocrosslinking was localized to the region of VP39 between residues Lys90 and Arg122. Peptide microsequencing and confirmatory mutagenesis identified the side-chain of Arg107 as the photocrosslinking site. Substitution of this residue with lysine abolished photocrosslinking entirely, consistent with the established RNA binding role of arginine in other RNA-binding proteins. This study provides clear evidence for a polyadenylylation-specific RNA-contact site on the surface of VP39, which is distinct from the RNA-binding methyltransferase "cleft" characterized in recent crystallographic and biochemical studies.
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Affiliation(s)
- L Deng
- Department of Biochemistry and Biophysics/Institute of Biosciences and Technology, Texas A&M University, Houston, TX, 77030, USA
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110
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Niewmierzycka A, Clarke S. S-Adenosylmethionine-dependent methylation in Saccharomyces cerevisiae. Identification of a novel protein arginine methyltransferase. J Biol Chem 1999; 274:814-24. [PMID: 9873020 DOI: 10.1074/jbc.274.2.814] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We used sequence motifs conserved in S-adenosylmethionine-dependent methyltransferases to identify 26 putative methyltransferases from the complete genome of the yeast Saccharomyces cerevisiae. Seven sequences with the best matches to the methyltransferase consensus motifs were selected for further study. We prepared yeast disruption mutants of each of the genes encoding these sequences, and we found that disruption of the YJL125c gene is lethal, whereas disruptions of YCR047c and YDR140w lead to slow growth phenotypes. Normal growth was observed when the YDL201w, YDR465c, YHR209w, and YOR240w genes were disrupted. Initial analysis of protein methylation patterns of all mutants by amino acid analysis revealed that the YDR465c mutant has a defect in the methylation of the delta-nitrogen atom of arginine residues. We propose that YDR465c codes for the methyltransferase responsible for this recently characterized type of protein methylation, and we designate the enzyme as Rmt2 (protein arginine methyltransferase). In addition, we show that the methylation of susceptible residues in Rmt2 substrates is likely to take place on nascent polypeptide chains and that these substrates exist in the cell as fully methylated species. Interestingly, Rmt2 has 27% sequence identity over 138 amino acids to the mammalian guanidinoacetate N-methyltransferase, an enzyme responsible for methylating the delta-nitrogen of the small molecule guanidinoacetate.
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Affiliation(s)
- A Niewmierzycka
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, California 90095-1569, USA
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111
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Tran PH, Korszun ZR, Cerritelli S, Springhorn SS, Lacks SA. Crystal structure of the DpnM DNA adenine methyltransferase from the DpnII restriction system of streptococcus pneumoniae bound to S-adenosylmethionine. Structure 1998; 6:1563-75. [PMID: 9862809 DOI: 10.1016/s0969-2126(98)00154-3] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND . Methyltransferases (Mtases) catalyze the transfer of methyl groups from S-adenosylmethionine (AdoMet) to a variety of small molecular and macromolecular substrates. These enzymes contain a characteristic alpha/beta structural fold. Four groups of DNA Mtases have been defined and representative structures have been determined for three groups. DpnM is a DNA Mtase that acts on adenine N6 in the sequence GATC; the enzyme represents group alpha DNA Mtases, for which no structures are known. RESULTS . The structure of DpnM in complex with AdoMet was determined at 1.80 A resolution. The protein comprises a consensus Mtase fold with a helical cluster insert. DpnM binds AdoMet in a similar manner to most other Mtases and the enzyme contains a hollow that can accommodate DNA. The helical cluster supports a shelf within the hollow that may recognize the target sequence. Modeling studies indicate a potential site for binding the target adenine, everted from the DNA helix. Comparison of the DpnM structure and sequences of group alpha DNA Mtases indicates that the group is a genetically related family. Structural comparisons show DpnM to be most similar to a small-molecule Mtase and then to macromolecular Mtases, although several dehydrogenases show greater similarity than one DNA Mtase. CONCLUSIONS . DpnM, and by extension the DpnM family or group alpha Mtases, contains the consensus fold and AdoMet-binding motifs found in most Mtases. Structural considerations suggest that macromolecular Mtases evolved from small-molecule Mtases, with different groups of DNA Mtases evolving independently. Mtases may have evolved from dehydrogenases. Comparison of these enzymes indicates that in protein evolution, the structural fold is most highly conserved, then function and lastly sequence.
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Affiliation(s)
- P H Tran
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973,USA
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112
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Vázquez MI, Rivas G, Cregut D, Serrano L, Esteban M. The vaccinia virus 14-kilodalton (A27L) fusion protein forms a triple coiled-coil structure and interacts with the 21-kilodalton (A17L) virus membrane protein through a C-terminal alpha-helix. J Virol 1998; 72:10126-37. [PMID: 9811753 PMCID: PMC110549 DOI: 10.1128/jvi.72.12.10126-10137.1998] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The vaccinia virus 14-kDa protein (encoded by the A27L gene) plays an important role in the biology of the virus, acting in virus-to-cell and cell-to-cell fusions. The protein is located on the surface of the intracellular mature virus form and is essential for both the release of extracellular enveloped virus from the cells and virus spread. Sequence analysis predicts the existence of four regions in this protein: a structureless region from amino acids 1 to 28, a helical region from residues 29 to 37, a triple coiled-coil helical region from residues 44 to 72, and a Leu zipper motif at the C terminus. Circular dichroism spectroscopy, analytical ultracentrifugation, and chemical cross-linking studies of the purified wild-type protein and several mutant forms, lacking one or more of the above regions or with point mutations, support the above-described structural division of the 14-kDa protein. The two contiguous cysteine residues at positions 71 and 72 are not responsible for the formation of 14-kDa protein trimers. The location of hydrophobic residues at the a and d positions on a helical wheel and of charged amino acids in adjacent positions, e and g, suggests that the hydrophobic and ionic interactions in the triple coiled-coil helical region are involved in oligomer formation. This conjecture was supported by the construction of a three-helix bundle model and molecular dynamics. Binding assays with purified proteins expressed in Escherichia coli and cytoplasmic extracts from cells infected with a virus that does not produce the 14-kDa protein during infection (VVindA27L) show that the 21-kDa protein (encoded by the A17L gene) is the specific viral binding partner and identify the putative Leu zipper, the predicted third alpha-helix on the C terminus of the 14-kDa protein, as the region involved in protein binding. These findings were confirmed in vivo, following transfection of animal cells with plasmid vectors expressing mutant forms of the 14-kDa protein and infected with VVindA27L. We find the structural organization of 14kDa to be similar to that of other fusion proteins, such as hemagglutinin of influenza virus and gp41 of human immunodeficiency virus, except for the presence of a protein-anchoring domain instead of a transmembrane domain. Based on our observations, we have established a structural model of the 14-kDa protein.
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Affiliation(s)
- M I Vázquez
- Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma, 28049 Madrid, Spain
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113
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Reeve AM, Breazeale SD, Townsend CA. Purification, characterization, and cloning of an S-adenosylmethionine-dependent 3-amino-3-carboxypropyltransferase in nocardicin biosynthesis. J Biol Chem 1998; 273:30695-703. [PMID: 9804844 DOI: 10.1074/jbc.273.46.30695] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
S-Adenosylmethionine:nocardicin 3-amino-3-carboxypropyltransferase catalyzes the biosynthetically rare transfer of the 3-amino-3-carboxypropyl moiety from S-adenosylmethionine to a phenolic site in the beta-lactam substrates nocardicin E, F, and G, a late step of the biosynthesis of the monocyclic beta-lactam antibiotic nocardicin A. Whereas a number of conventional methods were ineffective in purifying the transferase, it was successfully obtained by two complementary affinity chromatography steps that took advantage of the two substrate-two product reaction scheme. S-Adenosylhomocysteine-agarose selected enzymes that utilize S-adenosylmethionine, and a second column, nocardicin A-agarose, specifically bound the desired transferase to yield the enzyme as a single band of 38 kDa on a silver-stained SDS-polyacrylamide gel. The transferase is active as a monomer and exhibits sequential kinetics. Further kinetic characterization of this protein is described and its role in the biosynthesis of nocardicin A discussed. The gene encoding this transferase was cloned from a sublibrary of Nocardia uniformis DNA. Translation gave a protein of deduced mass 32,386 Da which showed weak homology to small molecule methyltransferases. However, three correctly disposed signature motifs characteristic of these enzymes were observed.
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Affiliation(s)
- A M Reeve
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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114
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Lau AY, Schärer OD, Samson L, Verdine GL, Ellenberger T. Crystal structure of a human alkylbase-DNA repair enzyme complexed to DNA: mechanisms for nucleotide flipping and base excision. Cell 1998; 95:249-58. [PMID: 9790531 DOI: 10.1016/s0092-8674(00)81755-9] [Citation(s) in RCA: 225] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
DNA N-glycosylases are base excision-repair proteins that locate and cleave damaged bases from DNA as the first step in restoring the genetic blueprint. The human enzyme 3-methyladenine DNA glycosylase removes a diverse group of damaged bases from DNA, including cytotoxic and mutagenic alkylation adducts of purines. We report the crystal structure of human 3-methyladenine DNA glycosylase complexed to a mechanism-based pyrrolidine inhibitor. The enzyme has intercalated into the minor groove of DNA, causing the abasic pyrrolidine nucleotide to flip into the enzyme active site, where a bound water is poised for nucleophilic attack. The structure shows an elegant means of exposing a nucleotide for base excision as well as a network of residues that could catalyze the in-line displacement of a damaged base from the phosphodeoxyribose backbone.
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Affiliation(s)
- A Y Lau
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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115
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O'Reilly EK, Wang Z, French R, Kao CC. Interactions between the structural domains of the RNA replication proteins of plant-infecting RNA viruses. J Virol 1998; 72:7160-9. [PMID: 9696810 PMCID: PMC109938 DOI: 10.1128/jvi.72.9.7160-7169.1998] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Brome mosaic virus (BMV), a positive-strand RNA virus, encodes two replication proteins: the 2a protein, which contains polymerase-like sequences, and the 1a protein, with N-terminal putative capping and C-terminal helicase-like sequences. These two proteins are part of a multisubunit complex which is necessary for viral RNA replication. We have previously shown that the yeast two-hybrid assay consistently duplicated results obtained from in vivo RNA replication assays and biochemical assays of protein-protein interaction, thus permitting the identification of additional interacting domains. We now map an interaction found to take place between two 1a proteins. Using previously characterized 1a mutants, a perfect correlation was found between the in vivo phenotypes of these mutants and their abilities to interact with wild-type 1a (wt1a) and each other. Western blot analysis revealed that the stabilities of many of the noninteracting mutant proteins were similar to that of wt1a. Deletion analysis of 1a revealed that the N-terminal 515 residues of the 1a protein are required and sufficient for 1a-1a interaction. This intermolecular interaction between the putative capping domain and itself was detected in another tripartite RNA virus, cucumber mosaic virus (CMV), suggesting that the 1a-1a interaction is a feature necessary for the replication of tripartite RNA viruses. The boundaries for various activities are placed in the context of the predicted secondary structures of several 1a-like proteins of members of the alphavirus-like superfamily. Additionally, we found a novel interaction between the putative capping and helicase-like portions of the BMV and CMV 1a proteins. Our cumulative data suggest a working model for the assembly of the BMV RNA replicase.
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Affiliation(s)
- E K O'Reilly
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA
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116
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Roth M, Helm-Kruse S, Friedrich T, Jeltsch A. Functional roles of conserved amino acid residues in DNA methyltransferases investigated by site-directed mutagenesis of the EcoRV adenine-N6-methyltransferase. J Biol Chem 1998; 273:17333-42. [PMID: 9651316 DOI: 10.1074/jbc.273.28.17333] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
All DNA methyltransferases (MTases) have similar catalytic domains containing nine blocks of conserved amino acid residues. We have investigated by site-directed mutagenesis the function of 17 conserved residues in the EcoRV alpha-adenine-N6-DNA methyltransferase. The structure of this class of MTases has been predicted recently. The variants were characterized with respect to their catalytic activities and their abilities to bind to DNA and the S-adenosylmethionine (AdoMet) cofactor. Amino acids located in motifs X, I, and II are shown to be involved in AdoMet binding (Lys16, Glu37, Phe39, and Asp58). Some of the mutants defective in AdoMet binding are also impaired in DNA binding, suggesting allosteric interactions between the AdoMet and DNA binding site. Asp78 (motif III), which was supposed to form a hydrogen bond to the AdoMet on the basis of the structure predictions, turned out not to be important for AdoMet binding, suggesting that motif III has not been identified correctly. R128A and N130A, having mutations in the putative DNA binding domain, are unable to bind to DNA. Residues located in motifs IV, V, VI, and VIII are involved in catalysis (Asp193, Tyr196, Asp211, Ser229, Trp231, and Tyr258), some of them presumably in binding the flipped target base, because mutations at these residues fail to significantly interfere with DNA and AdoMet binding but strongly reduce catalysis. Our results are in substantial agreement with the structure prediction for EcoRV alpha-adenine-N6-methyltransferase and x-ray structures of other MTases.
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Affiliation(s)
- M Roth
- Institut für Biochemie, Fachbereich Biologie, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
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117
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Gershon PD, Shi X, Hodel AE. Evidence that the RNA methylation and poly(A) polymerase stimulatory activities of vaccinia virus protein VP39 do not impinge upon one another. Virology 1998; 246:253-65. [PMID: 9657944 DOI: 10.1006/viro.1998.9209] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vaccinia protein VP39 has two RNA modifying activities. In monomeric form, it acts as an mRNA cap-specific 2'-O-methyltransferase, specifically modifying the ribose moiety of the first transcribed nucleotide of m7G-capped mRNA. In association with VP55, the catalytic subunit of the vaccinia poly(A) polymerase, VP39 facilitates the rapid elongation of poly(A) tails that are already greater than approximately 35 nt in length. Introducing new assays, we provide evidence that substrates for each of VP39's two activities do not detectably modulate the converse reaction and that VP39's 2'-O-methyltransferase activity is not significantly affected by its association with VP55. In an electrophoretic mobility shift assay, VP39 interacted with a short (5 nucleotide) RNA only when the latter was m7G-capped. Complexes with longer (22 nucleotide) RNAs were more stable (i.e., cap-independent) but were further stabilized by the presence of an m7G cap. An additional complex was observed at elevated RNA:protein molar ratios, indicating the presence of two RNA binding sites per VP39 molecule. Interaction at one of these sites was stabilized by the cap structure. Additional experiments indicated that RNA molecules undergoing poly(A) tail elongation by the VP55-VP39 heterodimer are not favored as cap-methylation substrates.
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Affiliation(s)
- P D Gershon
- Department of Biochemistry and Biophysics, Texas A&M University, Houston, USA.
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118
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Schubert HL, Wilson KS, Raux E, Woodcock SC, Warren MJ. The X-ray structure of a cobalamin biosynthetic enzyme, cobalt-precorrin-4 methyltransferase. NATURE STRUCTURAL BIOLOGY 1998; 5:585-92. [PMID: 9665173 DOI: 10.1038/846] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Biosynthesis of the corrin ring of vitamin B12 requires the action of six S-adenosyl-L-methionine (AdoMet) dependent transmethylases, closely related in sequence. The first X-ray structure of one of these, cobalt-precorrin-4 transmethylase, CbiF, from Bacillus megaterium has been determined to a resolution of 2.4 A. CbiF contains two alphabeta domains forming a trough in which S-adenosyl-L-homocysteine (AdoHcy) binds. The location of AdoHcy and a number of conserved residues, helps define the precorrin binding site. A second crystal form determined at 3.1 A resolution highlights the flexibility of two loops around this site. CbiF employs a unique mode of AdoHcy binding and represents a new class of transmethylase.
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Affiliation(s)
- H L Schubert
- Department of Chemistry, University of York, Heslington, UK
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119
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Rom E, Kim HC, Gingras AC, Marcotrigiano J, Favre D, Olsen H, Burley SK, Sonenberg N. Cloning and characterization of 4EHP, a novel mammalian eIF4E-related cap-binding protein. J Biol Chem 1998; 273:13104-9. [PMID: 9582349 DOI: 10.1074/jbc.273.21.13104] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
All eukaryotic mRNAs (except organellar) are capped at their 5' end. The cap structure (m7GpppN, where N is any nucleotide) is extremely important for the processing and translation of mRNA. Several cap-binding proteins that facilitate these processes have been characterized. Here we describe a novel human cytoplasmic protein that is 30% identical and 60% similar to the human translation initiation factor 4E (eIF4E). We demonstrate that this protein, named 4E Homologous Protein (4EHP), binds specifically to capped RNA in an ATP- and divalent ion-independent manner. The three-dimensional structure of 4EHP, as predicted by homology modeling, closely resembles that of eIF4E and site-directed mutagenesis analysis of 4EHP strongly suggests that it shares with eIF4E a common mechanism for cap binding. A putative function for 4EHP is discussed.
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Affiliation(s)
- E Rom
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G1Y6
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120
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Abstract
It is now generally accepted that the presence of 5-methylcytosine (5mC) in human DNA has both a genetic and an epigenetic effect on cellular development, differentiation and transformation. First, 5mC is more unstable than its unmethylated counterpart cytosine. Hydrolytic deamination of 5mC leads to a G/T mismatch and subsequently, if unrepaired, to a C-->T transition mutation. Sites of DNA methylation are mutational hotspots in many human tumors. Second, DNA methylation of promoter regions is often correlated with the down regulation of the corresponding gene. Both of these effects have fundamental consequences for basic functions of the cell like cellular differentiation, the development of cancer and possibly other diseases, and on the evolutionary process. Recent hypotheses also propose a role for methylation in the process of aging. In this review we will describe recent findings and hypotheses about the function of 5mC in DNA with the focus on its involvement in human carcinogenesis.
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Affiliation(s)
- C Schmutte
- Thomas Jefferson University, Kimmel Cancer Center, Philadelphia, PA 19107, USA
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121
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Gershon PD. mRNA 3′ End Formation by Vaccinia Virus: Mechanism of Action of a Heterodimeric Poly(A) Polymerase. ACTA ACUST UNITED AC 1998. [DOI: 10.1006/smvy.1997.0137] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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122
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123
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Hodel AE, Gershon PD, Quiocho FA. Structural basis for sequence-nonspecific recognition of 5'-capped mRNA by a cap-modifying enzyme. Mol Cell 1998; 1:443-7. [PMID: 9660928 DOI: 10.1016/s1097-2765(00)80044-1] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Sequence-nonspecific binding of RNA, recognition of a 7-methylguanosine 5' mRNA cap, and methylation of a nucleic acid backbone are three crucial and ubiquitous events in eukaryotic nucleic acid processing and function. These three events occur concurrently in the modification of vaccinia transcripts by the methyltransferase VP39. We report the crystal structure of a ternary complex comprising VP39, coenzyme product S-adenosylhomocysteine, and a 5' m7 G-capped, single-stranded RNA hexamer. This structure reveals a novel and general mechanism for sequence-non-specific recognition of the mRNA transcript in which the protein interacts solely with the sugar-phosphate backbone of a short, single-stranded RNA helix. This report represents the first direct and detailed view of a protein complexed with single-stranded RNA or 5'-capped mRNA.
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Affiliation(s)
- A E Hodel
- Howard Hughes Medical Institute, Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA
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124
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Ogawa H, Gomi T, Takusagawa F, Fujioka M. Structure, function and physiological role of glycine N-methyltransferase. Int J Biochem Cell Biol 1998; 30:13-26. [PMID: 9597750 DOI: 10.1016/s1357-2725(97)00105-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Glycine N-methyltransferase (EC 2.1.1.20) catalyzes the transfer of the methyl group of S-adenosylmethionine (AdoMet) to glycine to form S-adenosylhomocysteine and sarcosine. Unlike most AdoMet-dependent methyltransferases, glycine N-methyltransferase is a tetramer of identical subunits. Crystallography of recombinant rat glycine N-methyltransferase indicates that four nearly spherical subunits are arranged to form a flat, square tetramer with a large hole in the centre. The enzyme occurs abundantly in the livers of rat, rabbit and mouse. Glycine N-methyltransferases from rat, rabbit, human and pig livers are shown to have similar amino acid sequences and, with the enzymes from rat and rabbit livers, it is demonstrated that the N-terminal valine is acetylated. Glycine N-methyltransferases from livers exhibit sigmoidal rate behaviour with respect to AdoMet and hyperbolic behaviour with respect to glycine at all pH tested. However, recombinant rat glycine N-methyltransferase which lacks the N-terminal acetyl group shows no cooperativity toward AdoMet at neutral pH, suggesting that elimination of the positive charge at the N-terminus is required for cooperative behaviour. Glycine N-methyltransferase binds 5-methyltetrahydropteroylpentaglutamate tightly, resulting in inhibition of the catalytic activity. The nature of these unique functional features is discussed in the light of the three-dimensional structure of the enzyme. The tissue and subcellular localization of the enzyme and its possible role in methionine metabolism are reviewed.
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Affiliation(s)
- H Ogawa
- Department of Biochemistry, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan
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125
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Affiliation(s)
- M Bisaillon
- Département de Microbiologie et Immunologie, Université de Montréal, Station Centre-ville, Montréal, Québec, H3C 3J7, Canada
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126
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Shi X, Bernhardt TG, Wang SM, Gershon PD. The surface region of the bifunctional vaccinia RNA modifying protein VP39 that interfaces with Poly(A) polymerase is remote from the RNA binding cleft used for its mRNA 5' cap methylation function. J Biol Chem 1997; 272:23292-302. [PMID: 9287339 DOI: 10.1074/jbc.272.37.23292] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
VP39 is a single-domain, bifunctional viral protein, which acts at both ends of nascent mRNA. At the 5' end, it acts as a cap-specific 2'-O-methyltransferase. At the 3' end, it acts as a poly(A) polymerase processivity factor, requiring its direct association with poly(A) polymerase. Although crystallographic and biochemical data show the catalytic center and associated binding sites for VP39's methyltransferase function to be juxtaposed around a superficial cleft on the protein surface, surface regions required for VP39's mRNA 3' end modifying functions are not known. Here, we identify a surface region that interfaces directly with poly(A) polymerase, taking three independent approaches: (i) development of a direct in vitro dimerization assay, which is applied to numerous VP39 point mutants; (ii) identification of sites within VP39 that become protected from protease cleavage upon dimerization and further mutagenesis based upon these data; (iii) site-specific photo-cross-linking of VP39 to VP55. We find that the dimerization interface lies on a surface region remote from the methyltransferase cleft and contains a 3-5-residue "hot-spot," which is very sensitive to amino acid substitutions. Various other sites within VP39 consistently became hypersensitive to protease cleavage upon interaction with VP55, indicating the occurrence of extensive conformational changes.
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Affiliation(s)
- X Shi
- Institute of Biosciences and Technology/Department of Biochemistry and Biophysics, Texas A&M University, Houston, Texas 77030-3303, USA
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127
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Abstract
The 5' end of each polymerase II transcript is capped by a methylated guanosine triphosphate. The cap earmarks the mRNA for subsequent processing and nucleocytoplasmic transport, protects the mRNA from degradation and promotes efficient initiation of protein synthesis. The recently solved structures of capping enzymes and cap-protein complexes shed light on how the 5' ends of mRNAs are modified, and reveals the mechanisms by which the cap is recognized and how it functions in a diverse range of processes.
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Affiliation(s)
- G Varani
- MRC Laboratory of Molecular Biology, Cambridge, UK.
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128
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Marcotrigiano J, Gingras AC, Sonenberg N, Burley SK. Cocrystal structure of the messenger RNA 5' cap-binding protein (eIF4E) bound to 7-methyl-GDP. Cell 1997; 89:951-61. [PMID: 9200613 DOI: 10.1016/s0092-8674(00)80280-9] [Citation(s) in RCA: 505] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The X-ray structure of the eukaryotic translation initiation factor 4E (eIF4E), bound to 7-methyl-GDP, has been determined at 2.2 A resolution. eIF4E recognizes 5' 7-methyl-G(5')ppp(5')N mRNA caps during the rate-limiting initiation step of translation. The protein resembles a cupped hand and consists of a curved, 8-stranded antiparallel beta sheet, backed by three long alpha helices. 7-methyl-GDP binds in a narrow cap-binding slot on the molecule's concave surface, where 7-methyl-guanine recognition is mediated by base sandwiching between two conserved tryptophans, plus formation of three hydrogen bonds and a van der Waals contact between its N7-methyl group and a third conserved tryptophan. The convex dorsal surface of the molecule displays a phylogenetically conserved hydrophobic/acidic portion, which may interact with other translation initiation factors and regulatory proteins.
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Affiliation(s)
- J Marcotrigiano
- Laboratories of Molecular Biophysics, The Rockefeller University, New York, New York 10021, USA
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129
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Yu L, Petros AM, Schnuchel A, Zhong P, Severin JM, Walter K, Holzman TF, Fesik SW. Solution structure of an rRNA methyltransferase (ErmAM) that confers macrolide-lincosamide-streptogramin antibiotic resistance. NATURE STRUCTURAL BIOLOGY 1997; 4:483-9. [PMID: 9187657 DOI: 10.1038/nsb0697-483] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The Erm family of methyltransferases is responsible for the development of resistance to the macrolide-lincosamide-streptogramin type B (MLS) antibiotics. These enzymes methylate an adenine of 23S ribosomal RNA that prevents the MLS antibiotics from binding to the ribosome and exhibiting their antibacterial activity. Here we describe the three-dimensional structure of an Erm family member, ErmAM, as determined by NMR spectroscopy. The catalytic domain of ErmAM is structurally similar to that found in other methyltransferases and consists of a seven-stranded beta-sheet flanked by alpha-helices and a small two-stranded beta-sheet. In contrast to the catalytic domain, the substrate binding domain is different from other methyltransferases and adopts a novel fold that consists of four alpha-helices.
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Affiliation(s)
- L Yu
- Pharmaceutical Discovery Division, Abbott Laboratories, Abbott Park, Illinois 60064, USA
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130
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Abstract
Structural trees for large protein superfamilies, such as beta proteins with the aligned beta sheet packing, beta proteins with the orthogonal packing of alpha helices, two-layer and three-layer alpha/beta proteins, have been constructed. The structural motifs having unique overall folds and a unique handedness are taken as root structures of the trees. The larger protein structures of each superfamily are obtained by a stepwise addition of alpha helices and/or beta strands to the corresponding root motif, taking into account a restricted set of rules inferred from known principles of the protein structure. Among these rules, prohibition of crossing connections, attention to handedness and compactness, and a requirement for alpha helices to be packed in alpha-helical layers and beta strands in beta layers are the most important. Proteins and domains whose structures can be obtained by stepwise addition of alpha helices and/or beta strands to the same root motif can be grouped into one structural class or a superfamily. Proteins and domains found within branches of a structural tree can be grouped into subclasses or subfamilies. Levels of structural similarity between different proteins can easily be observed by visual inspection. Within one branch, protein structures having a higher position in the tree include the structures located lower. Proteins and domains of different branches have the structure located in the branching point as the common fold.
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Affiliation(s)
- A V Efimov
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region.
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131
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Antibiotics and RNA. NATURE STRUCTURAL BIOLOGY 1997; 4:421-2. [PMID: 9187643 DOI: 10.1038/nsb0697-421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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132
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Hodel AE, Gershon PD, Shi X, Wang SM, Quiocho FA. Specific protein recognition of an mRNA cap through its alkylated base. NATURE STRUCTURAL BIOLOGY 1997; 4:350-4. [PMID: 9145102 DOI: 10.1038/nsb0597-350] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The specific binding of N7-methylguanine cap analogues to the RNA methyltransferase VP39 was observed through X-ray crystallography, providing a prototypical structure for a complex between a protein and an mRNA 5' cap.
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133
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Djordjevic S, Stock AM. Crystal structure of the chemotaxis receptor methyltransferase CheR suggests a conserved structural motif for binding S-adenosylmethionine. Structure 1997; 5:545-58. [PMID: 9115443 DOI: 10.1016/s0969-2126(97)00210-4] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Flagellated bacteria swim towards favorable chemicals and away from deleterious ones. The sensing of chemoeffector gradients involves chemotaxis receptors, transmembrane proteins that detect stimuli through their periplasmic domains and transduce signals via their cytoplasmic domains to the downstream signaling components. Signaling outputs from chemotaxis receptors are influenced both by the binding of the chemoeffector ligand to the periplasmic domain and by methylation of specific glutamate residues on the cytoplasmic domain of the receptor. Methylation is catalyzed by CheR, an S-adenosylmethionine-dependent methyltransferase. CheR forms a tight complex with the receptor by binding a region of the receptors that is distinct from the methylation site. CheR belongs to a broad class of enzymes involved in the methylation of a variety of substrates. Until now, no structure from the class of protein methyltransferases has been characterized. RESULTS The structure of the Salmonella typhimurium chemotaxis receptor methyltransferase CheR bound to S-adenosylhomocysteine, a product and inhibitor of the methylation reaction, has been determined at 2.0 A resolution. The structure reveals CheR to be a two-domain protein, with a smaller N-terminal helical domain linked through a single polypeptide connection to a larger C-terminal alpha/beta domain. The C-terminal domain has the characteristics of a nucleotide-binding fold, with an insertion of a small antiparallel beta sheet subdomain. The S-adenosylhomocysteine-binding site is formed mainly by the large domain, with contributions from residues within the N-terminal domain and the linker region. CONCLUSIONS The CheR structure shares some structural similarities with small molecule DNA and RNA methyltransferases, despite a lack of sequence similarity among them. In particular, there is significant structural preservation of the S-adenosylmethionine-binding clefts; the specific length and conformation of a loop in the alpha/beta domain seems to be required for S-adenosylmethionine binding within these enzymes. Unique structural features of CheR, such as the beta subdomain, are probably necessary for CheR's specific interaction with its substrates, the bacterial chemotaxis receptors.
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Affiliation(s)
- S Djordjevic
- Howard Hughes Medical, Institute Center for Advanced Biotechnology and Medicine, Department of Biochemistry, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey, 08854, USA
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134
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Yoshida T, Tsunoda A, Koide H, Hoshina T. Flow Pattern and Electrical Conductance on a Planar Solid Oxide Fuel Cell. JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 1997. [DOI: 10.1252/jcej.30.677] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Atsushi Tsunoda
- Corporate Research & Development Laboratory, TONEN Corporation
| | - Hideto Koide
- Corporate Research & Development Laboratory, TONEN Corporation
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135
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Ahola T, Laakkonen P, Vihinen H, Kääriäinen L. Critical residues of Semliki Forest virus RNA capping enzyme involved in methyltransferase and guanylyltransferase-like activities. J Virol 1997; 71:392-7. [PMID: 8985362 PMCID: PMC191063 DOI: 10.1128/jvi.71.1.392-397.1997] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Semliki Forest virus (SFV) replicase protein nsP1 has methyltransferase (MT) and guanylyltransferase-like (GT) activities, which are involved in the capping of viral mRNAs. MT catalyzes the transfer of the methyl group from S-adenosylmethionine (AdoMet) to position 7 of GTP, and this reaction is followed by GT-catalyzed formation of the covalent complex m7GMP-nsP1. These reactions are virus specific and thus potential targets for inhibitors of virus replication. We have mutated residues of SFV nsP1, which are conserved in related proteins of the large alphavirus-like superfamily. Mutations of D64, D90, R93, C135, C142, and Y249 to alanine destroyed or greatly reduced the MT activity of nsP1. All MT-negative mutants lost also the GT activity, confirming that methylation of GTP is an essential prerequisite for the synthesis of the covalent guanylate complex. Mutation of H38 prevented the GT reaction without destroying MT activity. Conservation of residues essential for both reactions in the alphavirus-like superfamily implies that they use a capping mechanism similar to that for the alphaviruses. Residues D64 and D90 were necessary for AdoMet binding, as measured by UV cross-linking. Secondary structure predictions of nsP1 and other proteins of the superfamily place these residues in positions corresponding to AdoMet-binding sites of cellular methyltransferases, suggesting that they all may be structurally related.
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Affiliation(s)
- T Ahola
- Institute of Biotechnology, University of Helsinki, Finland.
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136
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Dixon MM, Huang S, Matthews RG, Ludwig M. The structure of the C-terminal domain of methionine synthase: presenting S-adenosylmethionine for reductive methylation of B12. Structure 1996; 4:1263-75. [PMID: 8939751 DOI: 10.1016/s0969-2126(96)00135-9] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND In both mammalian and microbial species, B12-dependent methionine synthase catalyzes methyl transfer from methyltetrahydrofolate (CH3-H4folate) to homocysteine. The B12 (cobalamin) cofactor plays an essential role in this reaction, accepting the methyl group from CH3-H4folate to form methylcob(III)alamin and in turn donating the methyl group to homocysteine to generate methionine and cob(I)alamin. Occasionally the highly reactive cob(I)alamin intermediate is oxidized to the catalytically inactive cob(II)alamin form. Reactivation to sustain enzyme activity is achieved by a reductive methylation, requiring S-adenosylmethionine (AdoMet) as the methyl donor and, in Esherichia coli, flavodoxin as an electron donor. The intact system is controlled and organized so that AdoMet, rather than methyltetrahydrofolate, is the methyl donor in the reactivation reaction. AdoMet is not wasted as a methyl donor in the catalytic cycle in which methionine is synthesized from homocysteine. The structures of the AdoMet binding site and the cobalamin-binding domains (previously determined) provide a starting point for understanding the methyl transfer reactions of methionine synthase. RESULTS We report the crystal structure of the 38 kDa C-terminal fragment of E.coli methionine synthase that comprises the AdoMet-binding site and is essential for reactivation. The structure, which includes residues 901-1227 of methionine synthase, is a C-shaped single domain whose central feature is a bent antiparallel betasheet. Database searches indicate that the observed polypeptide has no close relatives. AdoMet binds near the center of the inner surface of the domain and is held in place by both side chain and backbone interactions. CONCLUSIONS The conformation of bound AdoMet, and the interactions that determine its binding, differ from those found in other AdoMet-dependent enzymes. The sequence Arg-x-x-x-Gly-Tyr is critical for the binding of AdoMet to methionine synthase. The position of bound AdoMet suggests that large areas of the C-terminal and cobalamin-binding fragments must come in contact in order to transfer the methyl group of AdoMet to cobalamin. The catalytic and activation cycles may be turned off and on by alternating physical separation and approach of the reactants.
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Affiliation(s)
- M M Dixon
- Biophysics Research Division, University of Michigan, 930 N. University, Ann Arbor, MI 48109-1055, USA.
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137
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Robert Liddington CB, Frederick C. Paper alert. Structure 1996. [DOI: 10.1016/s0969-2126(96)00080-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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138
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Abstract
The structures of two DNA cytosine methyltransferases reveal two novel methods of gaining access to the substrate cytosine residue, both of which involve eversion of the cytosine in a process that may require DNA bending. In one instance there is also widespread base shuffling and distortion of the DNA.
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Affiliation(s)
- H C Nelson
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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