scholarly journals Metal-free class Ie ribonucleotide reductase from pathogens initiates catalysis with a tyrosine-derived dihydroxyphenylalanine radical

2018 ◽  
Vol 115 (40) ◽  
pp. 10022-10027 ◽  
Author(s):  
Elizabeth J. Blaesi ◽  
Gavin M. Palowitch ◽  
Kai Hu ◽  
Amelia J. Kim ◽  
Hannah R. Rose ◽  
...  
Keyword(s):  
Ribonucleotide Reductase ◽  
Metal Ion ◽  
Pathogenic Bacteria ◽  
Cysteine Residue ◽  
Class I ◽  
Tyrosyl Radical ◽  
Human Pathogens ◽  
Α Subunit ◽  
Metal Free ◽  
Iron Deprivation

All cells obtain 2′-deoxyribonucleotides for DNA synthesis through the activity of a ribonucleotide reductase (RNR). The class I RNRs found in humans and pathogenic bacteria differ in (i) use of Fe(II), Mn(II), or both for activation of the dinuclear-metallocofactor subunit, β; (ii) reaction of the reduced dimetal center with dioxygen or superoxide for this activation; (iii) requirement (or lack thereof) for a flavoprotein activase, NrdI, to provide the superoxide from O2; and (iv) use of either a stable tyrosyl radical or a high-valent dimetal cluster to initiate each turnover by oxidizing a cysteine residue in the α subunit to a radical (Cys•). The use of manganese by bacterial class I, subclass b-d RNRs, which contrasts with the exclusive use of iron by the eukaryotic Ia enzymes, appears to be a countermeasure of certain pathogens against iron deprivation imposed by their hosts. Here, we report a metal-free type of class I RNR (subclass e) from two human pathogens. The Cys• in its α subunit is generated by a stable, tyrosine-derived dihydroxyphenylalanine radical (DOPA•) in β. The three-electron oxidation producing DOPA• occurs inEscherichia colionly if the β is coexpressed with the NrdI activase encoded adjacently in the pathogen genome. The independence of this new RNR from transition metals, or the requirement for a single metal ion only transiently for activation, may afford the pathogens an even more potent countermeasure against transition metal-directed innate immunity.

scholarly journals Solution Structure of the dATP-Inactivated Class I Ribonucleotide Reductase From Leeuwenhoekiella blandensis by SAXS and Cryo-Electron Microscopy

2021 ◽  
Vol 8 ◽  
Author(s):  
Mahmudul Hasan ◽  
Ipsita Banerjee ◽  
Inna Rozman Grinberg ◽  
Britt-Marie Sjöberg ◽  
Derek T. Logan
Keyword(s):  
Ribonucleotide Reductase ◽  
Solution Structure ◽  
Three Dimensional ◽  
Class I ◽  
Structural Basis ◽  
Α Subunit ◽  
Cryo Electron Microscopy ◽  
N Terminus ◽  
Small Domain ◽  
Essential Enzyme

The essential enzyme ribonucleotide reductase (RNR) is highly regulated both at the level of overall activity and substrate specificity. Studies of class I, aerobic RNRs have shown that overall activity is downregulated by the binding of dATP to a small domain known as the ATP-cone often found at the N-terminus of RNR subunits, causing oligomerization that prevents formation of a necessary α2β2 complex between the catalytic (α2) and radical generating (β2) subunits. In some relatively rare organisms with RNRs of the subclass NrdAi, the ATP-cone is found at the N-terminus of the β subunit rather than more commonly the α subunit. Binding of dATP to the ATP-cone in β results in formation of an unusual β4 tetramer. However, the structural basis for how the formation of the active complex is hindered by such oligomerization has not been studied. Here we analyse the low-resolution three-dimensional structures of the separate subunits of an RNR from subclass NrdAi, as well as the α4β4 octamer that forms in the presence of dATP. The results reveal a type of oligomer not previously seen for any class of RNR and suggest a mechanism for how binding of dATP to the ATP-cone switches off catalysis by sterically preventing formation of the asymmetrical α2β2 complex.

scholarly journals In vitro activities of novel catecholate siderophores against Plasmodium falciparum.

1996 ◽  
Vol 40 (9) ◽  
pp. 2094-2098 ◽  
Author(s):  
B Pradines ◽  
F Ramiandrasoa ◽  
L K Basco ◽  
L Bricard ◽  
G Kunesch ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Mechanism Of Action ◽  
Ribonucleotide Reductase ◽  
Antimalarial Activity ◽  
Iron Chelators ◽  
Resistant Clone ◽  
Iron Deprivation ◽  
Level Of Activity ◽  
Susceptible Clone

The activities of novel iron chelators, alone and in combination with chloroquine, quinine, or artemether, were evaluated in vitro against susceptible and resistant clones of Plasmodium falciparum with a semimicroassay system. N4-nonyl,N1,N8-bis(2,3-dihydroxybenzoyl) spermidine hydrobromide (compound 7) demonstrated the highest level of activity: 170 nM against a chloroquine-susceptible clone and 1 microM against a chloroquine-resistant clone (50% inhibitory concentrations). Compounds 6, 8, and 10 showed antimalarial activity with 50% inhibitory concentrations of about 1 microM. Compound 7 had no effect on the activities of chloroquine, quinine, and artemether against either clone, and compound 8 did not enhance the schizontocidal action of either chloroquine or quinine against the chloroquine-resistant clone. The incubation of compound 7 with FeCI3 suppressed or decreased the in vitro antimalarial activity of compound 7, while no effect was observed with incubation of compound 7 with CuSO4 and ZnSO4. These results suggest that iron deprivation may be the main mechanism of action of compound 7 against the malarial parasites. Chelator compounds 7 and 8 primarily affected trophozoite stages, probably by influencing the activity of ribonucleotide reductase, and thus inhibiting DNA synthesis.

scholarly journals TO STUDY THE ANTIBACTERIAL ACTIVITY OF VARIOUS EXTRACTS OF CLAUSENA DENTATA (WILLD.) ROEM.

2019 ◽  
pp. 69-73
Author(s):  
ANNAMALAI MADURAM ◽  
RAJU KAMARAJ
Keyword(s):  
Antibacterial Activity ◽  
Tamil Nadu ◽  
Pathogenic Bacteria ◽  
Volatile Oil ◽  
Stem Bark ◽  
Salmonella Typhi ◽  
Chloroform Extract ◽  
Klebsiella Pneumonia ◽  
Human Pathogens ◽  
Human Pathogenic Bacteria

Objectives: The objectives of the study were to study the antibacterial activity for the various extracts of Clausena dentata against human pathogens. Clausena (Rutaceae) is a genus of about 23 species of unarmed trees and shrubs. The stem bark of C. dentata is used in veterinary medicine for the treatment of wounds and sprains. Even though C. dentata has a lot of potential medical uses, the study of microbiological properties is very scarce. Methods: The plant C. dentata was collected from Kadagaman, near Tiruvannamalai, Tamil Nadu, India, and authenticated by Centre for Advanced Study in Botany, University of Madras, Chennai. The dry powder of stem bark was extracted with hexane, chloroform, and methanol. The extracts were subjected to qualitative phytochemical screening and antibacterial activity against human pathogenic bacteria such as Escherichia coli, Salmonella Typhi, Klebsiella pneumonia, Vibrio cholerae, and Staphylococcus aureus and compared with ciprofloxacin. Results: Qualitative chemical tests revealed the presence of various phytochemicals such as alkaloids, glycosides, carbohydrate, proteins and amino acids, phytosterols, and volatile oil. The antibacterial activity result reveals that all the extracts were are more active against V. cholerae. The activity against Pseudomonas aeruginosa was mild. Conclusion: The activity against V. cholerae was comparable with that of 5 μg/mL ciprofloxacin at the concentration of C. dentata 40 μg/mL. The orders of antibacterial activity against human pathogenic bacteria are hexane, methanol, and chloroform extract of C. dentata.

scholarly journals Antimicrobial Activities of Marine Sponge-Associated Bacteria

2021 ◽  
Vol 9 (1) ◽  
pp. 171
Author(s):  
Yitayal S. Anteneh ◽  
Qi Yang ◽  
Melissa H. Brown ◽  
Christopher M. M. Franco
Keyword(s):  
Pathogenic Bacteria ◽  
South Australia ◽  
Multidrug Resistant ◽  
Antimicrobial Activities ◽  
Marine Sponges ◽  
Bioactive Metabolites ◽  
Human Pathogens ◽  
Sponge Associated Bacteria ◽  
Microbial Symbionts ◽  
Bacteria And Fungi

The misuse and overuse of antibiotics have led to the emergence of multidrug-resistant microorganisms, which decreases the chance of treating those infected with existing antibiotics. This resistance calls for the search of new antimicrobials from prolific producers of novel natural products including marine sponges. Many of the novel active compounds reported from sponges have originated from their microbial symbionts. Therefore, this study aims to screen for bioactive metabolites from bacteria isolated from sponges. Twelve sponge samples were collected from South Australian marine environments and grown on seven isolation media under four incubation conditions; a total of 1234 bacterial isolates were obtained. Of these, 169 bacteria were tested in media optimized for production of antimicrobial metabolites and screened against eleven human pathogens. Seventy bacteria were found to be active against at least one test bacterial or fungal pathogen, while 37% of the tested bacteria showed activity against Staphylococcus aureus including methicillin-resistant strains and antifungal activity was produced by 21% the isolates. A potential novel active compound was purified possessing inhibitory activity against S. aureus. Using 16S rRNA, the strain was identified as Streptomyces sp. Our study highlights that the marine sponges of South Australia are a rich source of abundant and diverse bacteria producing metabolites with antimicrobial activities against human pathogenic bacteria and fungi.

scholarly journals Interactions between the Escherichia coli cAMP receptor protein and the C-terminal domain of the α subunit of RNA polymerase at Class I promoters

1999 ◽  
Vol 337 (3) ◽  
pp. 415-423 ◽  
Author(s):  
Emma C. LAW ◽  
Nigel J. SAVERY ◽  
Stephen J. W. BUSBY
Keyword(s):  
Escherichia Coli ◽  
Rna Polymerase ◽  
Transcription Initiation ◽  
Class I ◽  
Receptor Protein ◽  
Camp Receptor Protein ◽  
Α Subunit ◽  
Terminal Domain ◽  
Up Elements ◽  
Camp Receptor

The Escherichia coli cAMP receptor protein (CRP) is a factor that activates transcription at over 100 target promoters. At Class I CRP-dependent promoters, CRP binds immediately upstream of RNA polymerase and activates transcription by making direct contacts with the C-terminal domain of the RNA polymerase α subunit (αCTD). Since αCTD is also known to interact with DNA sequence elements (known as UP elements), we have constructed a series of semi-synthetic Class I CRP-dependent promoters, carrying both a consensus DNA-binding site for CRP and a UP element at different positions. We previously showed that, at these promoters, the CRP–αCTD interaction and the CRP–UP element interaction contribute independently and additively to transcription initiation. In this study, we show that the two halves of the UP element can function independently, and that, in the presence of the UP element, the best location for the DNA site for CRP is position -69.5. This suggests that, at Class I CRP-dependent promoters where the DNA site for CRP is located at position -61.5, the two αCTDs of RNA polymerase are not optimally positioned. Two experiments to test this hypothesis are presented.

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