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Pseudomonas aeruginosa Polynucleotide Phosphorylase Controls Tolerance to Aminoglycoside Antibiotics by Regulating the MexXY Multidrug Efflux Pump. Antimicrob Agents Chemother 2021; 65:AAC.01846-20. [PMID: 33257447 DOI: 10.1128/aac.01846-20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Accepted: 11/18/2020] [Indexed: 01/01/2023] Open
Abstract
Pseudomonas aeruginosa is an opportunistic pathogen that shows high intrinsic resistance to a variety of antibiotics. The MexX-MexY-OprM efflux pump plays an important role in bacterial resistance to aminoglycoside antibiotics. Polynucleotide phosphorylase (PNPase) is a highly conserved exonuclease that plays important roles in RNA processing and the bacterial response to environmental stresses. Previously, we demonstrated that PNPase controls the tolerance to fluoroquinolone antibiotics by influencing the production of pyocin in P. aeruginosa In this study, we found that mutation of the PNPase-encoding gene (pnp) in P. aeruginosa increases bacterial tolerance to aminoglycoside antibiotics. We further demonstrate that the upregulation of the mexXY genes is responsible for the increased tolerance of the pnp mutant. Furthermore, our experimental results revealed that PNPase controls the translation of the armZ mRNA through its 5' untranslated region (UTR). ArmZ had previously been shown to positively regulate the expression of mexXY Therefore, our results revealed a novel role of PNPase in the regulation of armZ and subsequently the MexXY efflux pump.
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2
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Gonzalez-Rivera JC, Orr AA, Engels SM, Jakubowski JM, Sherman MW, O'Connor KN, Matteson T, Woodcock BC, Contreras LM, Tamamis P. Computational evolution of an RNA-binding protein towards enhanced oxidized-RNA binding. Comput Struct Biotechnol J 2020; 18:137-152. [PMID: 31988703 PMCID: PMC6965710 DOI: 10.1016/j.csbj.2019.12.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2019] [Revised: 12/06/2019] [Accepted: 12/06/2019] [Indexed: 12/02/2022] Open
Abstract
The oxidation of RNA has been implicated in the development of many diseases. Among the four ribonucleotides, guanosine is the most susceptible to oxidation, resulting in the formation of 8-oxo-7,8-dihydroguanosine (8-oxoG). Despite the limited knowledge about how cells regulate the detrimental effects of oxidized RNA, cellular factors involved in its regulation have begun to be identified. One of these factors is polynucleotide phosphorylase (PNPase), a multifunctional enzyme implicated in RNA turnover. In the present study, we have examined the interaction of PNPase with 8-oxoG in atomic detail to provide insights into the mechanism of 8-oxoG discrimination. We hypothesized that PNPase subunits cooperate to form a binding site using the dynamic SFF loop within the central channel of the PNPase homotrimer. We evolved this site using a novel approach that initially screened mutants from a library of beneficial mutations and assessed their interactions using multi-nanosecond Molecular Dynamics simulations. We found that evolving this single site resulted in a fold change increase in 8-oxoG affinity between 1.2 and 1.5 and/or selectivity between 1.5 and 1.9. In addition to the improvement in 8-oxoG binding, complementation of K12 Δpnp with plasmids expressing mutant PNPases caused increased cell tolerance to H2O2. This observation provides a clear link between molecular discrimination of RNA oxidation and cell survival. Moreover, this study provides a framework for the manipulation of modified-RNA protein readers, which has potential application in synthetic biology and epitranscriptomics.
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Affiliation(s)
- Juan C. Gonzalez-Rivera
- McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States
| | - Asuka A. Orr
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU Room 200, College Station, TX 77843, United States
| | - Sean M. Engels
- McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States
| | - Joseph M. Jakubowski
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU Room 200, College Station, TX 77843, United States
| | - Mark W. Sherman
- Institute of Cellular and Molecular Biology, The University of Texas at Austin, 100 E 24th Street, Stop A5000, Austin, TX 78712, United States
| | - Katherine N. O'Connor
- McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States
| | - Tomas Matteson
- Institute of Cellular and Molecular Biology, The University of Texas at Austin, 100 E 24th Street, Stop A5000, Austin, TX 78712, United States
| | - Brendan C. Woodcock
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU Room 200, College Station, TX 77843, United States
| | - Lydia M. Contreras
- McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States
- Institute of Cellular and Molecular Biology, The University of Texas at Austin, 100 E 24th Street, Stop A5000, Austin, TX 78712, United States
- Corresponding authors at: McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States (L.M. Contreras).
| | - Phanourios Tamamis
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU Room 200, College Station, TX 77843, United States
- Corresponding authors at: McKetta Department of Chemical Engineering, The University of Texas, 200 E. Dean Keeton Street Stop C0400, Austin, TX 78712, United States (L.M. Contreras).
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3
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Cameron TA, Matz LM, Sinha D, De Lay NR. Polynucleotide phosphorylase promotes the stability and function of Hfq-binding sRNAs by degrading target mRNA-derived fragments. Nucleic Acids Res 2019; 47:8821-8837. [PMID: 31329973 PMCID: PMC7145675 DOI: 10.1093/nar/gkz616] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 07/02/2019] [Accepted: 07/11/2019] [Indexed: 01/14/2023] Open
Abstract
In many Gram-negative and some Gram-positive bacteria, small regulatory RNAs (sRNAs) that bind the RNA chaperone Hfq have a pivotal role in modulating virulence, stress responses, metabolism and biofilm formation. These sRNAs recognize transcripts through base-pairing, and sRNA–mRNA annealing consequently alters the translation and/or stability of transcripts leading to changes in gene expression. We have previously found that the highly conserved 3′-to-5′ exoribonuclease polynucleotide phosphorylase (PNPase) has an indispensable role in paradoxically stabilizing Hfq-bound sRNAs and promoting their function in gene regulation in Escherichia coli. Here, we report that PNPase contributes to the degradation of specific short mRNA fragments, the majority of which bind Hfq and are derived from targets of sRNAs. Specifically, we found that these mRNA-derived fragments accumulate in the absence of PNPase or its exoribonuclease activity and interact with PNPase. Additionally, we show that mutations in hfq or in the seed pairing region of some sRNAs eliminated the requirement of PNPase for their stability. Altogether, our results are consistent with a model that PNPase degrades mRNA-derived fragments that could otherwise deplete cells of Hfq-binding sRNAs through pairing-mediated decay.
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Affiliation(s)
- Todd A Cameron
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center, Houston, TX 77030, USA
| | - Lisa M Matz
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center, Houston, TX 77030, USA
| | - Dhriti Sinha
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center, Houston, TX 77030, USA
| | - Nicholas R De Lay
- Department of Microbiology and Molecular Genetics, McGovern Medical School, The University of Texas Health Science Center, Houston, TX 77030, USA.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center, Houston, TX 77030, USA
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4
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Malla S, Li Z. Functions of Conserved Domains of Human Polynucleotide Phosphorylase on RNA Oxidation. ACTA ACUST UNITED AC 2019; 3:62-67. [PMID: 32123871 PMCID: PMC7051052 DOI: 10.36959/584/448] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human polynucleotide phosphorylase (hPNPase), an exoribonuclease that is primarily localized in mitochondria, plays an important role in reducing oxidized RNA and protecting cells under oxidative stress conditions. hPNPase contains two catalytic domains (RPH1 and RPH2) and two RNA binding domains (KH and S1), and an N-terminal mitochondrial translocation signal (MTS). In this study, we examined the potential roles of each domain in hPNPase function on controlling RNA oxidative damage. DNA encoding full-length hPNPase and its domain-deletion mutants were introduced into HeLa cells, and the levels of an oxidized RNA lesion, 8-hydroxyguanosine (8-oxo-Guo) were determined in mitochondrial and cytoplasmic RNA under oxidative stress conditions. Our study showed that the S1 RNA binding domain is crucial for reducing 8-oxo-Guo in both cytoplasm and mitochondria, while the MTS is required for 8-oxo-Guo reduction in mitochondria.
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Affiliation(s)
- Sulochan Malla
- Department of Biomedical Science, Florida Atlantic University, USA
| | - Zhongwei Li
- Department of Biomedical Science, Florida Atlantic University, USA
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5
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Fan Z, Chen H, Li M, Pan X, Fu W, Ren H, Chen R, Bai F, Jin Y, Cheng Z, Jin S, Wu W. Pseudomonas aeruginosa Polynucleotide Phosphorylase Contributes to Ciprofloxacin Resistance by Regulating PrtR. Front Microbiol 2019; 10:1762. [PMID: 31417536 PMCID: PMC6682600 DOI: 10.3389/fmicb.2019.01762] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Accepted: 07/16/2019] [Indexed: 12/17/2022] Open
Abstract
Pseudomonas aeruginosa is an opportunistic bacterial pathogen that causes various acute and chronic infections. It is intrinsically resistant to a variety of antibiotics. However, production of pyocins during SOS response sensitizes P. aeruginosa to quinolone antibiotics by inducing cell lysis. The polynucleotide phosphorylase (PNPase) is a conserved phosphate-dependent 3′–5′ exonuclease that plays an important role in bacterial response to environmental stresses and pathogenesis by influencing mRNA and small RNA stabilities. Previously, we demonstrated that PNPase controls the type III and type VI secretion systems in P. aeruginosa. In this study, we found that mutation of the PNPase coding gene (pnp) increases the bacterial resistance to ciprofloxacin. Gene expression analyses revealed that the expression of pyocin biosynthesis genes is decreased in the pnp mutant. PrtR, a negative regulator of pyocin biosynthesis genes, is upregulated in the pnp mutant. We further demonstrated that PNPase represses the expression of PrtR on the post-transcriptional level. A fragment containing 43 nucleotides of the 5′ untranslated region was found to be involved in the PNPase mediated regulation of PrtR. Overall, our results reveled a novel layer of regulation on the pyocin biosynthesis by the PNPase in P. aeruginosa.
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Affiliation(s)
- Zheng Fan
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Hao Chen
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Mei Li
- Meishan Product Quality Supervision and Inspection Institute and National Pickle Quality Inspection Center, Meishan, China
| | - Xiaolei Pan
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Weixin Fu
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Huan Ren
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Ronghao Chen
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Fang Bai
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Yongxin Jin
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Zhihui Cheng
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
| | - Shouguang Jin
- Department of Molecular Genetics and Microbiology, College of Medicine, University of Florida, Gainesville, FL, United States
| | - Weihui Wu
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin, China
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Cameron TA, Matz LM, De Lay NR. Polynucleotide phosphorylase: Not merely an RNase but a pivotal post-transcriptional regulator. PLoS Genet 2018; 14:e1007654. [PMID: 30307990 PMCID: PMC6181284 DOI: 10.1371/journal.pgen.1007654] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Almost 60 years ago, Severo Ochoa was awarded the Nobel Prize in Physiology or Medicine for his discovery of the enzymatic synthesis of RNA by polynucleotide phosphorylase (PNPase). Although this discovery provided an important tool for deciphering the genetic code, subsequent work revealed that the predominant function of PNPase in bacteria and eukaryotes is catalyzing the reverse reaction, i.e., the release of ribonucleotides from RNA. PNPase has a crucial role in RNA metabolism in bacteria and eukaryotes mainly through its roles in processing and degrading RNAs, but additional functions in RNA metabolism have recently been reported for this enzyme. Here, we discuss these established and noncanonical functions for PNPase and the possibility that the major impact of PNPase on cell physiology is through its unorthodox roles.
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Affiliation(s)
- Todd A. Cameron
- Department of Microbiology and Molecular Genetics, McGovern Medical School, University of Texas Health Science Center, Houston, Texas, United States of America
| | - Lisa M. Matz
- Department of Microbiology and Molecular Genetics, McGovern Medical School, University of Texas Health Science Center, Houston, Texas, United States of America
| | - Nicholas R. De Lay
- Department of Microbiology and Molecular Genetics, McGovern Medical School, University of Texas Health Science Center, Houston, Texas, United States of America
- MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center, Houston, Texas, United States of America
- * E-mail:
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7
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Orr AA, Gonzalez-Rivera JC, Wilson M, Bhikha PR, Wang D, Contreras LM, Tamamis P. A high-throughput and rapid computational method for screening of RNA post-transcriptional modifications that can be recognized by target proteins. Methods 2018; 143:34-47. [DOI: 10.1016/j.ymeth.2018.01.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Revised: 01/14/2018] [Accepted: 01/26/2018] [Indexed: 12/25/2022] Open
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8
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Chen R, Weng Y, Zhu F, Jin Y, Liu C, Pan X, Xia B, Cheng Z, Jin S, Wu W. Polynucleotide Phosphorylase Regulates Multiple Virulence Factors and the Stabilities of Small RNAs RsmY/Z in Pseudomonas aeruginosa. Front Microbiol 2016; 7:247. [PMID: 26973625 PMCID: PMC4773659 DOI: 10.3389/fmicb.2016.00247] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 02/15/2016] [Indexed: 12/17/2022] Open
Abstract
Post-transcriptional regulation enables bacteria to quickly response to environmental stresses. Polynucleotide phosphorylase (PNPase), which contains an N-terminal catalytic core and C-terminal RNA binding KH-S1 domains, is involved in RNA processing. Here we demonstrate that in Pseudomonas aeruginosa the KH-S1 domains of PNPase are required for the type III secretion system (T3SS) and bacterial virulence. Transcriptome analysis revealed a pleiotropic role of PNPase in gene regulation. Particularly, the RNA level of exsA was decreased in the ΔKH-S1 mutant, which was responsible for the reduced T3SS expression. Meanwhile, the pilus biosynthesis genes were down regulated and the type VI secretion system (T6SS) genes were up regulated in the ΔKH-S1 mutant, which were caused by increased levels of small RNAs, RsmY, and RsmZ. Further studies revealed that deletion of the KH-S1 domains did not affect the transcription of RsmY/Z, but increased their stabilities. An in vivo pull-down and in vitro electrophoretic mobility shift assay (EMSA) demonstrated a direct interaction between RsmY/Z and the KH-S1 fragment. Overall, this study reveals the roles of PNPase in the regulation of virulence factors and stabilities of small RNAs in P. aeruginosa.
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Affiliation(s)
- Ronghao Chen
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Yuding Weng
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Feng Zhu
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Yongxin Jin
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Chang Liu
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Xiaolei Pan
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Bin Xia
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Zhihui Cheng
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
| | - Shouguang Jin
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai UniversityTianjin, China; Department of Molecular Genetics and Microbiology, College of Medicine, University of FloridaGainesville, FL, USA
| | - Weihui Wu
- State Key Laboratory of Medicinal Chemical Biology, Key Laboratory of Molecular Microbiology and Technology of the Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University Tianjin, China
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9
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Bandyra KJ, Sinha D, Syrjanen J, Luisi BF, De Lay NR. The ribonuclease polynucleotide phosphorylase can interact with small regulatory RNAs in both protective and degradative modes. RNA (NEW YORK, N.Y.) 2016; 22:360-72. [PMID: 26759452 PMCID: PMC4748814 DOI: 10.1261/rna.052886.115] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 11/29/2015] [Indexed: 05/22/2023]
Abstract
In all bacterial species examined thus far, small regulatory RNAs (sRNAs) contribute to intricate patterns of dynamic genetic regulation. Many of the actions of these nucleic acids are mediated by well-characterized chaperones such as the Hfq protein, but genetic screens have also recently identified the 3'-to-5' exoribonuclease polynucleotide phosphorylase (PNPase) as an unexpected stabilizer and facilitator of sRNAs in vivo. To understand how a ribonuclease might mediate these effects, we tested the interactions of PNPase with sRNAs and found that the enzyme can readily degrade these nucleic acids in vitro but, nonetheless, copurifies from cell extracts with the same sRNAs without discernible degradation or modification to their 3' ends, suggesting that the associated RNA is protected against the destructive activity of the ribonuclease. In vitro, PNPase, Hfq, and sRNA can form a ternary complex in which the ribonuclease plays a nondestructive, structural role. Such ternary complexes might be formed transiently in vivo, but could help to stabilize particular sRNAs and remodel their population on Hfq. Taken together, our results indicate that PNPase can be programmed to act on RNA in either destructive or stabilizing modes in vivo and may form complex, protective ribonucleoprotein assemblies that shape the landscape of sRNAs available for action.
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Affiliation(s)
- Katarzyna J Bandyra
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
| | - Dhriti Sinha
- Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston, Texas 77030, USA
| | - Johanna Syrjanen
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
| | - Ben F Luisi
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
| | - Nicholas R De Lay
- Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston, Texas 77030, USA Graduate School of Biomedical Sciences, University of Texas Health Science Center, Houston, Texas 77030, USA
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RNase III-Independent Autogenous Regulation of Escherichia coli Polynucleotide Phosphorylase via Translational Repression. J Bacteriol 2015; 197:1931-8. [PMID: 25825432 DOI: 10.1128/jb.00105-15] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 03/23/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The complex posttranscriptional regulation mechanism of the Escherichia coli pnp gene, which encodes the phosphorolytic exoribonuclease polynucleotide phosphorylase (PNPase), involves two endoribonucleases, namely, RNase III and RNase E, and PNPase itself, which thus autoregulates its own expression. The models proposed for pnp autoregulation posit that the target of PNPase is a mature pnp mRNA previously processed at its 5' end by RNase III, rather than the primary pnp transcript (RNase III-dependent models), and that PNPase activity eventually leads to pnp mRNA degradation by RNase E. However, some published data suggest that pnp expression may also be regulated through a PNPase-dependent, RNase III-independent mechanism. To address this issue, we constructed isogenic Δpnp rnc(+) and Δpnp Δrnc strains with a chromosomal pnp-lacZ translational fusion and measured β-galactosidase activity in the absence and presence of PNPase expressed by a plasmid. Our results show that PNPase also regulates its own expression via a reversible RNase III-independent pathway acting upstream from the RNase III-dependent branch. This pathway requires the PNPase RNA binding domains KH and S1 but not its phosphorolytic activity. We suggest that the RNase III-independent autoregulation of PNPase occurs at the level of translational repression, possibly by competition for pnp primary transcript between PNPase and the ribosomal protein S1. IMPORTANCE In Escherichia coli, polynucleotide phosphorylase (PNPase, encoded by pnp) posttranscriptionally regulates its own expression. The two models proposed so far posit a two-step mechanism in which RNase III, by cutting the leader region of the pnp primary transcript, creates the substrate for PNPase regulatory activity, eventually leading to pnp mRNA degradation by RNase E. In this work, we provide evidence supporting an additional pathway for PNPase autogenous regulation in which PNPase acts as a translational repressor independently of RNase III cleavage. Our data make a new contribution to the understanding of the regulatory mechanism of pnp mRNA, a process long since considered a paradigmatic example of posttranscriptional regulation at the level of mRNA stability.
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11
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Carzaniga T, Mazzantini E, Nardini M, Regonesi ME, Greco C, Briani F, De Gioia L, Dehò G, Tortora P. A conserved loop in polynucleotide phosphorylase (PNPase) essential for both RNA and ADP/phosphate binding. Biochimie 2013; 97:49-59. [PMID: 24075876 DOI: 10.1016/j.biochi.2013.09.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 09/16/2013] [Indexed: 11/27/2022]
Abstract
Polynucleotide phosphorylase (PNPase) reversibly catalyzes RNA phosphorolysis and polymerization of nucleoside diphosphates. Its homotrimeric structure forms a central channel where RNA is accommodated. Each protomer core is formed by two paralogous RNase PH domains: PNPase1, whose function is largely unknown, hosts a conserved FFRR loop interacting with RNA, whereas PNPase2 bears the putative catalytic site, ∼20 Å away from the FFRR loop. To date, little is known regarding PNPase catalytic mechanism. We analyzed the kinetic properties of two Escherichia coli PNPase mutants in the FFRR loop (R79A and R80A), which exhibited a dramatic increase in Km for ADP/Pi binding, but not for poly(A), suggesting that the two residues may be essential for binding ADP and Pi. However, both mutants were severely impaired in shifting RNA electrophoretic mobility, implying that the two arginines contribute also to RNA binding. Additional interactions between RNA and other PNPase domains (such as KH and S1) may preserve the enzymatic activity in R79A and R80A mutants. Inspection of enzyme structure showed that PNPase has evolved a long-range acting hydrogen bonding network that connects the FFRR loop with the catalytic site via the F380 residue. This hypothesis was supported by mutation analysis. Phylogenetic analysis of PNPase domains and RNase PH suggests that such network is a unique feature of PNPase1 domain, which coevolved with the paralogous PNPase2 domain.
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Affiliation(s)
- Thomas Carzaniga
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan 20133, Italy.
| | - Elisa Mazzantini
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Milan 20126, Italy.
| | - Marco Nardini
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan 20133, Italy.
| | - Maria Elena Regonesi
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Milan 20126, Italy.
| | - Claudio Greco
- Dipartimento di Scienze dell'ambiente e del territorio e di Scienze della terra, Università degli Studi di Milano-Bicocca, Milan 20126, Italy.
| | - Federica Briani
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan 20133, Italy.
| | - Luca De Gioia
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Milan 20126, Italy.
| | - Gianni Dehò
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan 20133, Italy.
| | - Paolo Tortora
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Milan 20126, Italy.
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Hardwick SW, Gubbey T, Hug I, Jenal U, Luisi BF. Crystal structure of Caulobacter crescentus polynucleotide phosphorylase reveals a mechanism of RNA substrate channelling and RNA degradosome assembly. Open Biol 2013; 2:120028. [PMID: 22724061 PMCID: PMC3376730 DOI: 10.1098/rsob.120028] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Accepted: 03/12/2012] [Indexed: 11/20/2022] Open
Abstract
Polynucleotide phosphorylase (PNPase) is an exoribonuclease that cleaves single-stranded RNA substrates with 3′–5′ directionality and processive behaviour. Its ring-like, trimeric architecture creates a central channel where phosphorolytic active sites reside. One face of the ring is decorated with RNA-binding K-homology (KH) and S1 domains, but exactly how these domains help to direct the 3′ end of single-stranded RNA substrates towards the active sites is an unsolved puzzle. Insight into this process is provided by our crystal structures of RNA-bound and apo Caulobacter crescentus PNPase. In the RNA-free form, the S1 domains adopt a ‘splayed’ conformation that may facilitate capture of RNA substrates. In the RNA-bound structure, the three KH domains collectively close upon the RNA and direct the 3′ end towards a constricted aperture at the entrance of the central channel. The KH domains make non-equivalent interactions with the RNA, and there is a marked asymmetry within the catalytic core of the enzyme. On the basis of these data, we propose that structural non-equivalence, induced upon RNA binding, helps to channel substrate to the active sites through mechanical ratcheting. Structural and biochemical analyses also reveal the basis for PNPase association with RNase E in the multi-enzyme RNA degradosome assembly of the α-proteobacteria.
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Affiliation(s)
- Steven W Hardwick
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK
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S1 and KH domains of polynucleotide phosphorylase determine the efficiency of RNA binding and autoregulation. J Bacteriol 2013; 195:2021-31. [PMID: 23457244 DOI: 10.1128/jb.00062-13] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To better understand the roles of the KH and S1 domains in RNA binding and polynucleotide phosphorylase (PNPase) autoregulation, we have identified and investigated key residues in these domains. A convenient pnp::lacZ fusion reporter strain was used to assess autoregulation by mutant PNPase proteins lacking the KH and/or S1 domains or containing point mutations in those domains. Mutant enzymes were purified and studied by using in vitro band shift and phosphorolysis assays to gauge binding and enzymatic activity. We show that reductions in substrate affinity accompany impairment of PNPase autoregulation. A remarkably strong correlation was observed between β-galactosidase levels reflecting autoregulation and apparent KD values for the binding of a model RNA substrate. These data show that both the KH and S1 domains of PNPase play critical roles in substrate binding and autoregulation. The findings are discussed in the context of the structure, binding sites, and function of PNPase.
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