Ribonucleotide Reductases

Nordlund, P.; Reichard, Peter

doi:10.1146/annurev.biochem.75.103004.142443

Cited by 984 publications

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“…It catalyzes the reduction of ribonucleotides (nucleoside triphosphates [NTPs]) to their corresponding 2=-deoxyribonucleotides (deoxynucleoside triphosphates [dNTPs]) and therefore plays an essential role in DNA synthesis and repair. Three RNR classes (classes I, II, and III) exist; these classes exhibit different primary structures, subunit cofactor requirements, and quaternary three-dimensional (3D) structures, but they all are allosterically regulated and share similar catalytic mechanisms (1,2). Class I RNRs are oxygendependent enzymes that occur in eubacteria, eukaryotes, and some viruses.…”

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confidence: 99%

“…nrdD and nrdG form an operon and encode the catalytic NrdD subunit and the activating protein NrdG, respectively. This system works only under strict anaerobic conditions because oxygen is toxic to these enzymes (1,2). Notably, the distribution of the different RNR classes is difficult to elucidate, as the different bacterial phylogenetic groups do not display any common RNR combinations.…”

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Ribonucleotide Reductase NrdR as a Novel Regulator for Motility and Chemotaxis during Adherent-Invasive Escherichia coli Infection

et al. 2015

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A critical step in the life cycle of all organisms is the duplication of the genetic material during cell division. Ribonucleotide reductases (RNRs) are essential enzymes for this step because they control the de novo production of the deoxyribonucleotides required for DNA synthesis and repair. Enterobacteriaceae have three functional classes of RNRs (Ia, Ib, and III), which are transcribed from separate operons and encoded by the genes nrdAB, nrdHIEF, and nrdDG, respectively. Here, we investigated the role of RNRs in the virulence of adherent-invasive Escherichia coli (AIEC) isolated from Crohn's disease (CD) patients. Interestingly, the LF82 strain of AIEC harbors four different RNRs (two class Ia, one class Ib, and one class III). Although the E. coli RNR enzymes have been extensively characterized both biochemically and enzymatically, little is known about their roles during bacterial infection. We found that RNR expression was modified in AIEC LF82 bacteria during cell infection, suggesting that RNRs play an important role in AIEC virulence. Knockout of the nrdR and nrdD genes, which encode a transcriptional regulator of RNRs and class III anaerobic RNR, respectively, decreased AIEC LF82's ability to colonize the gut mucosa of transgenic mice that express human CEACAM6 (carcinoembryonic antigen-related cell adhesion molecule 6). Microarray experiments demonstrated that NrdR plays an indirect role in AIEC virulence by interfering with bacterial motility and chemotaxis. Thus, the development of drugs targeting RNR classes, in particular NrdR and NrdD, could be a promising new strategy to control gut colonization by AIEC bacteria in CD patients.R ibonucleotide reductase (RNR) is an essential enzyme in all living organisms. It catalyzes the reduction of ribonucleotides (nucleoside triphosphates [NTPs]) to their corresponding 2=-deoxyribonucleotides (deoxynucleoside triphosphates [dNTPs]) and therefore plays an essential role in DNA synthesis and repair. Three RNR classes (classes I, II, and III) exist; these classes exhibit different primary structures, subunit cofactor requirements, and quaternary three-dimensional (3D) structures, but they all are allosterically regulated and share similar catalytic mechanisms (1, 2). Class I RNRs are oxygendependent enzymes that occur in eubacteria, eukaryotes, and some viruses. This class comprises two main subgroups (Ia and Ib). Class Ia RNRs are encoded by an operon containing nrdA and nrdB genes. These genes encode the NrdA subunit, which is catalytically and allosterically regulated, and the NrdB subunit, which possesses radical-generating activity. Class Ib RNRs are encoded by an operon containing the nrdH, nrdI, nrdE, and nrdF genes, which encode the corresponding specific redoxin NrdH, the activating subunit NrdI, the catalytic subunit NrdE, and the radical-generating subunit NrdF. Class III RNRs are present in facultative anaerobic and strict anaerobic microorganisms and use S-adenosylmethionine and iron-sulfur clusters in the NrdG accessory protein to create a stab...

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Ribonucleotide Reductase NrdR as a Novel Regulator for Motility and Chemotaxis during Adherent-Invasive Escherichia coli Infection

et al. 2015

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“…R2 is rate limiting for the enzymatic activity of RNR and its level is cell cycle dependent (Chabes and Thelander, 2000). However, an analogue of R2, p53R2 has recently been found that is not cell cycle dependent (Guittet et al, 2001;Nordlund and Reichard, 2006). p53R2 can substitute for R2 to form an active RNR enzyme capable of generating deoxyribonucleotides in resting cells or following DNA damage.…”

Section: Discussionmentioning

confidence: 99%

Expression of thymidylate synthase in human cells is an early G1 event regulated by CDK4 and p16INK4A but not E2F

2007

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Thymidylate synthase (TS) is the enzyme that catalyses the last step in de novo thymidylate synthesis. It is of interest clinically because it is an effective target for drugs such as 5-fluorouracil, often used in combination therapy. Despite a number of earlier reports indicating that TS is a cell cycle-dependent enzyme, this remains equivocal. Here, we show that in HCT116 cells synchronised by serum starvation, there is a clear dissociation between the expression of cyclin E (a well-characterised cell-cycle protein) and TS. Although both cyclin E and TS mRNA and protein increased during G 1 , TS upregulation was delayed. Moreover, TS levels did not decrease following S-phase completion while cyclin E decreased sharply. Similarly, clear differences were seen between cyclin E and TS as asynchronously growing HCT116 cells were growth-inhibited by low-serum treatment. In contrast to previous reports using rodent cells, adenovirus-mediated over-expression of E2F1 and cyclin E in three human cell lines had no effect on TS. Cell-cycle progression was blocked by treatment of cells with pharmacological inhibitors of CDK2 and CDK4 and by ectopic expression of p16INK4A. Whereas CDK2 inhibition had no effect on TS levels, inhibition of CDK4 was associated with decreased TS protein levels. These results provide the first evidence that drugs targeting CDK4 may be useful with anti-TS drugs as combination therapy for cancer.

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“…9 While the R1 subunit is expressed in quiescent cells, although at a low level, the R2 subunit expression is silenced. 10 Here, we report that HBV increases the dNTP pool for effective viral production in quiescent cells by directly targeting the R2 gene to induce unscheduled R2 expression without affecting cell cycle progression.…”

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Hepatitis B Virus Activates Deoxynucleotide Synthesis in Nondividing Hepatocytes by Targeting the R2 Gene

Cohen¹,

Adamovich²,

Reuven³

et al. 2010

Hepatology

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Hepatitis B virus (HBV) causes liver diseases from acute hepatitis to cirrhosis and liver cancer. Currently, more than 350 million people are chronic HBV carriers, with devastating prognosis. HBV is a small enveloped noncytopathic virus, containing a circular partially double-stranded DNA genome, and exhibits strong tropism for human liver cells. Infected individuals (acute and chronic) secrete about 10 7 to 10 11 virions per day to the bloodstream, with each infected cell releasing 50-300 viruses per day. HBV infects nondividing hepatocytes and replicates by reverse-transcribing the pregenomic RNA to DNA in the host cells. The level of deoxyribonucleotide triphosphates (dNTPs) in nondividing cells is too low to support viral replication and enable the high yield of secreted virions. Here, we report production of dNTPs by viral-dependent transcription activation of R2, the key component of ribonucleotide reductase (RNR), and show that this process is critical for the HBV life-cycle. This was found in an established HBV-positive cell line and was reproduced by HBV DNA-transduced cells, in both culture and mice. Furthermore, the viral hepatitis B X protein is essential in activating R2 expression by blocking access of Regulatory factor x1, a repressor of the R2 gene. Conclusion: Our findings demonstrate that the hepatitis B X protein is critical in infecting nonproliferating hepatocytes, which contain a low dNTP level. In addition, we provide molecular evidence for a new mechanism of HBV-host cell interaction where RNR-R2, a critical cell-cycle gene, is selectively activated in nonproliferating cells. This mechanism may set the stage for formulating a new category of anti-HBV drugs. (HEPATOLOGY 2010;51:1538-1546 H epatitis B virus (HBV) is a widespread pathogen responsible for acute and chronic hepatitis and is a causative factor of hepatocellular carcinoma (HCC). 1 HBV is a small-enveloped noncytopathic virus containing a circular partially doublestranded DNA genome, and exhibits strong tropism for human liver cells. 2 During replication, the viral polymerase reverse-transcribes the pregenomic RNA to DNA using deoxyribonucleotide triphosphates (dNTPs). HBV preferentially replicates in nondividing cells, 3 in which the concentration of dNTP is low, which raised the question whether dNTP concentration is adequate to support viral yield. The level of dNTPs in a nondividing adult liver cell is <0.4 lM. 4 The Michaelis constant (K m ) of the viral polymerase at a dNTP concentration of 0.4 lM is only 62%, whereas a 4 lM concentration gives 93.3% activity. 5 Furthermore, one hepatocyte produces 50-300 hepatitis B virions per day, 6 and because the HBV genome is approximately 3.2 kilobases, between 3 Â 10 5 to 2 Â 10 6 dNTPs are consumed per day in this process. Considering cell volume as 500 fL, 7 a resting cell contains approximately 1.2 Â 10 5 dNTP molecules. Thus, the total amount of dNTPs used for HBV production per day exceeds the amount found in a nondividing hepatocyte. Because HBV does not activate the cell cycl...

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Ribonucleotide Reductases

Cited by 984 publications

References 148 publications

Ribonucleotide Reductase NrdR as a Novel Regulator for Motility and Chemotaxis during Adherent-Invasive Escherichia coli Infection

Ribonucleotide Reductase NrdR as a Novel Regulator for Motility and Chemotaxis during Adherent-Invasive Escherichia coli Infection

Expression of thymidylate synthase in human cells is an early G1 event regulated by CDK4 and p16INK4A but not E2F

Hepatitis B Virus Activates Deoxynucleotide Synthesis in Nondividing Hepatocytes by Targeting the R2 Gene

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