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  • 1. Aurelius, Oskar
    et al.
    Johansson, Renzo
    Bågenholm, Viktoria
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Tholander, Fredrik
    Balhuizen, Alexander
    Beck, Tobias
    Sahlin, Margareta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mulliez, Etienne
    Logan, Derek T.
    The Crystal Structure of Thermotoga maritima Class III Ribonucleotide Reductase Lacks a Radical Cysteine Pre-Positioned in the Active Site2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 7, article id e0128199Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to deoxyribonucleotides, the building blocks for DNA synthesis, and are found in all but a few organisms. RNRs use radical chemistry to catalyze the reduction reaction. Despite RNR having evolved several mechanisms for generation of different kinds of essential radicals across a large evolutionary time frame, this initial radical is normally always channelled to a strictly conserved cysteine residue directly adjacent to the substrate for initiation of substrate reduction, and this cysteine has been found in the structures of all RNRs solved to date. We present the crystal structure of an anaerobic RNR from the extreme thermophile Thermotoga maritima (tmNrdD), alone and in several complexes, including with the allosteric effector dATP and its cognate substrate CTP. In the crystal structure of the enzyme as purified, tmNrdD lacks a cysteine for radical transfer to the substrate pre-positioned in the active site. Nevertheless activity assays using anaerobic cell extracts from T. maritima demonstrate that the class III RNR is enzymatically active. Other genetic and microbiological evidence is summarized indicating that the enzyme is important for T. maritima. Mutation of either of two cysteine residues in a disordered loop far from the active site results in inactive enzyme. We discuss the possible mechanisms for radical initiation of substrate reduction given the collected evidence from the crystal structure, our activity assays and other published work. Taken together, the results suggest either that initiation of substrate reduction may involve unprecedented conformational changes in the enzyme to bring one of these cysteine residues to the expected position, or that alternative routes for initiation of the RNR reduction reaction may exist. Finally, we present a phylogenetic analysis showing that the structure of tmNrdD is representative of a new RNR subclass IIIh, present in all Thermotoga species plus a wider group of bacteria from the distantly related phyla Firmicutes, Bacteroidetes and Proteobacteria.

  • 2.
    Björk Grimberg, Kristian
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Beskow, Anne
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Davis, Monica M.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Young, Patrick
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Basic Leucine Zipper Protein Cnc-C is a Substrate and Transcriptional Regulator of the Drosophila 26S Proteasome2011In: Molecular and Cellular Biology, ISSN 0270-7306, E-ISSN 1098-5549, Vol. 31, no 4, p. 897-909Article in journal (Refereed)
    Abstract [en]

    While the 26S proteasome is a key proteolytic complex, little is known about how proteasome levels are maintained in higher eukaryotic cells. Here we describe an RNA interference (RNAi) screen of Drosophila melanogaster that was used to identify transcription factors that may play a role in maintaining levels of the 26S proteasome. We used an RNAi library against 993 Drosophila transcription factor genes to identify genes whose suppression in Schneider 2 cells stabilized a ubiquitin-green fluorescent protein reporter protein. This screen identified Cnc (cap 'n' collar [CNC]; basic region leucine zipper) as a candidate transcriptional regulator of proteasome component expression. In fact, 20S proteasome activity was reduced in cells depleted of cnc. Immunoblot assays against proteasome components revealed a general decline in both 19S regulatory complex and 20S proteasome subunits after RNAi depletion of this transcription factor. Transcript-specific silencing revealed that the longest of the seven transcripts for the cnc gene, cnc-C, was needed for proteasome and p97 ATPase production. Quantitative reverse transcription-PCR confirmed the role of Cnc-C in activation of transcription of genes encoding proteasome components. Expression of a V5-His-tagged form of Cnc-C revealed that the transcription factor is itself a proteasome substrate that is stabilized when the proteasome is inhibited. We propose that this single cnc gene in Drosophila resembles the ancestral gene family of mammalian nuclear factor erythroid-derived 2-related transcription factors, which are essential in regulating oxidative stress and proteolysis.

  • 3.
    Ensterö, Mats
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Åkerborg, Örjan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Wang, Bei
    Furey, Terrence S
    Öhman, Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Lagergren, Jens
    A computational screen for site selective A-to-I editing detects novel sites in neuron specific Hu proteins2010In: BMC Bioinformatics, ISSN 1471-2105, E-ISSN 1471-2105, Vol. 11, no 6Article in journal (Refereed)
    Abstract [en]

    Background

    Several bioinformatic approaches have previously been used to find novel sites of ADAR mediated A-to-I RNA editing in human. These studies have discovered thousands of genes that are hyper-edited in their non-coding intronic regions, especially in alu retrotransposable elements, but very few substrates that are site-selectively edited in coding regions. Known RNA edited substrates suggest, however, that site selective A-to-I editing is particularly important for normal brain development in mammals.

    Results

    We have compiled a screen that enables the identification of new sites of site-selective editing, primarily in coding sequences. To avoid hyper-edited repeat regions, we applied our screen to the alu-free mouse genome. Focusing on the mouse also facilitated better experimental verification. To identify candidate sites of RNA editing, we first performed an explorative screen based on RNA structure and genomic sequence conservation. We further evaluated the results of the explorative screen by determining which transcripts were enriched for A-G mismatches between the genomic template and the expressed sequence since the editing product, inosine (I), is read as guanosine (G) by the translational machinery. For expressed sequences, we only considered coding regions to focus entirely on re-coding events. Lastly, we refined the results from the explorative screen using a novel scoring scheme based on characteristics for known A-to-I edited sites. The extent of editing in the final candidate genes was verified using total RNA from mouse brain and 454 sequencing.

    Conclusions

    Using this method, we identified and confirmed efficient editing at one site in the Gabra3 gene. Editing was also verified at several other novel sites within candidates predicted to be edited. Five of these sites are situated in genes coding for the neuron-specific RNA binding proteins HuB and HuD.

  • 4. Johansson, Renzo
    et al.
    Jonna, Venkateswara Rao
    Kumar, Rohit
    Nayeri, Niloofar
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hofer, Anders
    Logan, Derek T.
    Structural Mechanism of Allosteric Activity Regulation in a Ribonucleotide Reductase with Double ATP Cones2016In: Structure, ISSN 0969-2126, E-ISSN 1878-4186, Vol. 24, no 6, p. 906-917Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductases (RNRs) reduce ribonucleotides to deoxyribonucleotides. Their overall activity is stimulated by ATP and downregulated by dATP via a genetically mobile ATP cone domain mediating the formation of oligomeric complexes with varying quaternary structures. The crystal structure and solution X-ray scattering data of a novel dATP-induced homotetramer of the Pseudomonas aeruginosa class I RNR reveal the structural bases for its unique properties, namely one ATP cone that binds two dATP molecules and a second one that is non-functional, binding no nucleotides. Mutations in the observed tetramer interface ablate oligomerization and dATP-induced inhibition but not the ability to bind dATP. Sequence analysis shows that the novel type of ATP cone may be widespread in RNRs. The present study supports a scenario in which diverse mechanisms for allosteric activity regulation are gained and lost through acquisition and evolutionary erosion of different types of ATP cone.

  • 5. Jonna, Venkateswara Rao
    et al.
    Crona, Mikael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Rofougaran, Reza
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Johansson, Samuel
    Brännström, Kristoffer
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hofer, Anders
    Diversity in Overall Activity Regulation of Ribonucleotide Reductase2015In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 290, no 28, p. 17339-17348Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductase (RNR) catalyzes the reduction of ribonucleotides to the corresponding deoxyribonucleotides, which are used as building blocks for DNA replication and repair. This process is tightly regulated via two allosteric sites, the specificity site (s-site) and the overall activity site (a-site). The a-site resides in an N-terminal ATP cone domain that binds dATP or ATP and functions as an on/off switch, whereas the composite s-site binds ATP, dATP, dTTP, or dGTP and determines which substrate to reduce. There are three classes of RNRs, and class I RNRs consist of different combinations of alpha and beta subunits. In eukaryotic and Escherichia coli class I RNRs, dATP inhibits enzyme activity through the formation of inactive alpha(6) and alpha(4)beta(4) complexes, respectively. Here we show that the Pseudomonas aeruginosa class IRNR has a duplicated ATP cone domain and represents a third mechanism of overall activity regulation. Each alpha polypeptide binds three dATP molecules, and the N-terminal ATP cone is critical for binding two of the dATPs because a truncated protein lacking this cone could only bind dATP to its s-site. ATP activates the enzyme solely by preventing dATP from binding. The dATP-induced inactive form is an alpha(4) complex, which can interact with beta(2) to form a non-productive alpha(4)beta(2) complex. Other allosteric effectors induce a mixture of alpha(2) and alpha(4) forms, with the former being able to interact with beta(2) to form active alpha(2)beta(2) complexes. The unique features of the P. aeruginosa RNR are interesting both from evolutionary and drug discovery perspectives.

  • 6. Loderer, Christoph
    et al.
    Holmfeldt, Karin
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Linnaeus University, Sweden.
    Non-host class II ribonucleotide reductase in Thermus viruses: sequence adaptation and host interaction2019In: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 7, article id e6700Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductases (RNR) are essential enzymes for all known life forms. Their current taxonomic distribution suggests extensive horizontal gene transfer e.g., by processes involving viruses. To improve our understanding of the underlying processes, we characterized a monomeric class II RNR (NrdJm) enzyme from a Thermus virus, a subclass not present in any sequenced Thermus spp. genome. Phylogenetic analysis revealed a distant origin of the nrdJm gene with the most closely related sequences found in mesophiles or moderate thermophiles from the Firmicutes phylum. GC-content, codon usage and the ratio of coding to non-coding substitutions (dN/dS) suggest extensive adaptation of the gene in the virus in terms of nucleotide composition and amino acid sequence. The NrdJm enzyme is a monomeric B-12-dependent RNR with nucleoside triphosphate specificity. It exhibits a temperature optimum at 60-70 degrees C, which is in the range of the growth optimum of Thermus spp. Experiments in combination with the Thermus thermophilus thioredoxin system show that the enzyme is able to retrieve electrons from the host NADPH pool via host thioredoxin and thioredoxin reductases. This is different from other characterized viral RNRs such as T4 phage RNR, where a viral thioredoxin is present. We hence show that the monomeric class II RNR, present in Thermus viruses, was likely transferred from an organism phylogenetically distant from the one they were isolated from, and adapted to the new host in genetic signature and amino acids sequence.

  • 7.
    Loderer, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jonna, Venkateswara Rao
    Crona, Mikael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Rozman Grinberg, Inna
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sahlin, Margareta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hofer, Anders
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    A unique cysteine-rich zinc finger domain present in a majority of class II ribonucleotide reductases mediates catalytic turnover2017In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 292, no 46, p. 19044-19054Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to the corresponding deoxyribonucleotides, used in DNA synthesis and repair. Two different mechanisms help deliver the required electrons to the RNR active site. Formate can be used as reductant directly in the active site, or glutaredoxins or thioredoxins reduce a C-terminal cysteine pair, which then delivers the electrons to the active site. Here, we characterized a novel cysteine-rich C-terminal domain (CRD), which is present in most class II RNRs found in microbes. The NrdJd-type RNR from the bacterium Stackebrandtia nassauensis was used as a model enzyme. We show that the CRD is involved in both higher oligomeric state formation and electron transfer to the active site. The CRD-dependent formation of high oligomers, such as tetramers and hexamers, was induced by addition of dATP or dGTP, but not of dTTP or dCTP. The electron transfer was mediated by an array of six cysteine residues at the very C-terminal end, which also coordinated a zinc atom. The electron transfer can also occur between subunits, depending on the enzyme's oligomeric state. An investigation of the native reductant of the system revealed no interaction with glutaredoxins or thioredoxins, indicating that this class II RNR uses a different electron source. Our results indicate that the CRD has a crucial role in catalytic turnover and a potentially new terminal reduction mechanism and suggest that the CRD is important for the activities of many class II RNRs.

  • 8.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    The evolution of ribonucleotide reductases2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ribonucleotide reductase (RNR) catalyses the transformation of RNA building blocks, ribonucleotides, to DNA building blocks, deoxyribonucleotides. This is the only extant reaction pathway for de novo synthesis of DNA building blocks and the enzyme is thus necessary for life. RNR is found in all but a few organisms.

    There are three classes of RNR, all evolutionarily related. The classification is built on differences in generation of the radical that is central to the reaction. As a consequence, RNR classes have different operational constraints. Class I requires oxygen, while class III is poisoned by oxygen. Class II is independent of oxygen, but dependent on vitamin B12 and, hence, cobalt. This makes RNR interesting from an evolutionary as well as environmental point of view.

    RNR must have evolved before the transition from RNA encoded genomes to DNA encoded. The extant radical-based reaction is likely similar to the ancestral reaction, which entails that the ancestral enzyme was a protein and not an RNR.

    My results are consistent with both class II and III being present in the last universal common ancestor. Class I RNR evolved later, presumably once oxygen levels had risen. From commonalities in extant RNRs we can reconstruct their last common ancestor as an enzyme that 1) used a transient cysteine-radical in the reaction, 2) reduced all four ribonucleotides, 3) regulated which nucleotide was reduced after binding an effector nucleotide in the dimer interface of the enzyme and 4) had activity regulation through binding of a nucleotide to another part of the enzyme.

    The presence of a specific RNR class is likely to influence the environmental range of organisms, which makes horizontal transfer of RNR particularly interesting. Horizontal transfer of RNR genes is widespread, both between closely related organisms and between domains. For instance, all three classes are present in eukaryotes, but likely all three are results of horizontal transfer.

  • 9. Masson, Patrick
    et al.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Söderbom, Fredrik
    Young, Patrick
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Characterization of a REG/PA28 Proteasome Activator Homolog in Dictyostelium discoideum Indicates that the Ubiquitin- and ATP-Independent REG gamma Proteasome Is an Ancient Nuclear Protease2009In: Eukaryotic Cell, ISSN 1535-9778, E-ISSN 1535-9786, Vol. 8, no 6, p. 844-851Article in journal (Refereed)
    Abstract [en]

    The nuclear proteasome activator REG gamma/PA28 gamma is an ATP- and ubiquitin-independent activator of the 20S proteasome and has been proposed to degrade and thereby regulate both a key human oncogene, encoding the coactivator SRC-3/AIB1, and the cyclin-dependent kinase inhibitor p21 (Waf/Cip1). We report the identification and characterization of a PA28/REG homolog in Dictyostelium. Association of a recombinant Dictyostelium REG with the purified Dictyostelium 20S proteasome led to the preferential stimulation of the trypsin-like proteasome peptidase activity. Immunolocalization studies demonstrated that the proteasome activator is localized to the nucleus and is present in growing as well as starving Dictyostelium cells. Our results indicate that the Dictyostelium PA28/REG activator can stimulate both the trypsin-like and chymotrypsin-like activities of the 20S proteasome and supports the idea that the REG gamma-20S proteasome represents an early unique nuclear degradation pathway for eukaryotic cells.

  • 10. Navon, Ruth
    et al.
    Silberberg, Gilad
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Öhman, Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    A Comprehensive Survey of RNA Editing In Psychiatric Disorders Reveals Multiple Novel Editing Sites in Coding Regions2011Conference paper (Refereed)
  • 11.
    Neumann, Nadja
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Poole, Anthony M.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Comparative Genomic Evidence for a Complete Nuclear Pore Complex in the Last Eukaryotic Common Ancestor2010In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 10, p. e13241-Article in journal (Refereed)
    Abstract [en]

    Background: The Nuclear Pore Complex (NPC) facilitates molecular trafficking between nucleus and cytoplasm and is an integral feature of the eukaryote cell. It exhibits eight-fold rotational symmetry and is comprised of approximately 30 nucleoporins (Nups) in different stoichiometries. Nups are broadly conserved between yeast, vertebrates and plants, but few have been identified among other major eukaryotic groups. Methodology/Principal Findings: We screened for Nups across 60 eukaryote genomes and report that 19 Nups (spanning all major protein subcomplexes) are found in all eukaryote supergroups represented in our study (Opisthokonts, Amoebozoa, Viridiplantae, Chromalveolates and Excavates). Based on parsimony, between 23 and 26 of 31 Nups can be placed in LECA. Notably, they include central components of the anchoring system (Ndc1 and Gp210) indicating that the anchoring system did not evolve by convergence, as has previously been suggested. These results significantly extend earlier results and, importantly, unambiguously place a fully-fledged NPC in LECA. We also test the proposal that transmembrane Pom proteins in vertebrates and yeasts may account for their variant forms of mitosis (open mitoses in vertebrates, closed among yeasts). The distribution of homologues of vertebrate Pom121 and yeast Pom152 is not consistent with this suggestion, but the distribution of fungal Pom34 fits a scenario wherein it was integral to the evolution of closed mitosis in ascomycetes. We also report an updated screen for vesicle coating complexes, which share a common evolutionary origin with Nups, and can be traced back to LECA. Surprisingly, we find only three supergroup-level differences (one gain and two losses) between the constituents of COPI, COPII and Clathrin complexes. Conclusions/Significance: Our results indicate that all major protein subcomplexes in the Nuclear Pore Complex are traceable to the Last Eukaryotic Common Ancestor (LECA). In contrast to previous screens, we demonstrate that our conclusions hold regardless of the position of the root of the eukaryote tree.

  • 12. Poole, Anthony M.
    et al.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Linnaeus University, Sweden.
    Rytkoenen, Kalle T.
    The evolution of early cellular systems viewed through the lens of biological interactions2015In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 6, article id 1144Article in journal (Refereed)
    Abstract [en]

    The minimal cell concept represents a pragmatic approach to the question of how few genes are required to run a cell. This is a helpful way to build a parts-list, and has been more successful than attempts to deduce a minimal gene set for life by inferring the gene repertoire of the last universal common ancestor, as few genes trace back to this hypothetical ancestral state. However, the study of minimal cellular systems is the study of biological outliers where, by practical necessity, coevolutionary interactions are minimized or ignored. In this paper, we consider the biological context from which minimal genomes have been removed. For instance, some of the most reduced genomes are from endosymbionts and are the result of coevolutionary interactions with a host; few such organisms are free-living. As few, if any, biological systems exist in complete isolation, we expect that, as with modern life, early biological systems were part of an ecosystem, replete with organismal interactions. We favor refocusing discussions of the evolution of cellular systems on processes rather than gene counts. We therefore draw a distinction between a pragmatic minimal cell (an interesting engineering problem), a distributed genome (a system resulting from an evolutionary transition involving more than one cell) and the looser coevolutionary interactions that are ubiquitous in ecosystems. Finally, we consider the distributed genome and coevolutionary interactions between genomic entities in the context of early evolution.

  • 13.
    Rozman Grinberg, Inna
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hasan, Mahmudul
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Lund University, Sweden.
    Crona, Mikael
    Jonna, Venkateswara Rao
    Loderer, Chrishtoph
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sahlin, Margareta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Markova, Natalia
    Borovok, Ilya
    Berggren, Gustav
    Hofer, Anders
    Logan, Derek T.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Novel ATP-cone-driven allosteric regulation of ribonucleotide reductase via the radical-generating subunit2018In: eLIFE, E-ISSN 2050-084X, Vol. 7, article id e31529Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductases (RNRs) are key enzymes in DNA metabolism, with allosteric mechanisms controlling substrate specificity and overall activity. In RNRs, the activity master-switch, the ATP-cone, has been found exclusively in the catalytic subunit. In two class I RNR subclasses whose catalytic subunit lacks the ATP-cone, we discovered ATP-cones in the radical-generating subunit. The ATP-cone in the Leeuwenhoekiella blandensis radical-generating subunit regulates activity via quaternary structure induced by binding of nucleotides. ATP induces enzymatically competent dimers, whereas dATP induces non-productive tetramers, resulting in different holoenzymes. The tetramer forms by interactions between ATP-cones, shown by a 2.45 A crystal structure. We also present evidence for an (MnMnIV)-Mn-III metal center. In summary, lack of an ATP-cone domain in the catalytic subunit was compensated by transfer of the domain to the radical-generating subunit. To our knowledge, this represents the first observation of transfer of an allosteric domain between components of the same enzyme complex.

  • 14.
    Rozman Grinberg, Inna
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sahlin, Margareta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Crona, Mikael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Swedish Orphan Biovitrum AB, Sweden.
    Berggren, Gustav
    Hofer, Anders
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    A glutaredoxin domain fused to the radical-generating subunit of ribonucleotide reductase (RNR) functions as an efficient RNR reductant2018In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 293, no 41, p. 15889-15900Article in journal (Refereed)
    Abstract [en]

    Class I ribonucleotide reductase (RNR) consists of a catalytic subunit (NrdA) and a radical-generating subunit (NrdB) that together catalyze reduction of ribonucleotides to their corresponding deoxyribonucleotides. NrdB from the firmicute Facklamia ignava is a unique fusion protein with N-terminal addons of a glutaredoxin (Grx) domain followed by an ATP-binding domain, the ATP cone. Grx, usually encoded separately from the RNR operon, is a known RNR reductant. We show that the fused Grx domain functions as an efficient reductant of the F. ignava class I RNR via the common dithiol mechanism and, interestingly, also via a monothiol mechanism, although less efficiently. To our knowledge, a Grx that uses both of these two reaction mechanisms has not previously been observed with a native substrate. The ATP cone is in most RNRs an N-terminal domain of the catalytic subunit. It is an allosteric on/off switch promoting ribonucleotide reduction in the presence of ATP and inhibiting RNR activity in the presence of dATP. We found that dATP bound to the ATP cone of F. ignava NrdB promotes formation of tetramers that cannot form active complexes with NrdA. The ATP cone bound two dATP molecules but only one ATP molecule. F. ignava NrdB contains the recently identified radical-generating cofactor Mn-III/Mn-IV. We show that NrdA from F. ignava can form a catalytically competent RNR with the Mn-III/Mn-IV-containing NrdB from the flavobacterium Leeuwenhoekiella blandensis. In conclusion, F. ignava NrdB is fused with a Grx functioning as an RNR reductant and an ATP cone serving as an on/off switch.

  • 15.
    Silberberg, Gilad
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Navon, Ruth
    Öhman, Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Deregulation of the A-to-I RNA editing mechanism in psychiatric disorders2012In: Human Molecular Genetics, ISSN 0964-6906, E-ISSN 1460-2083, Vol. 21, no 2, p. 311-321Article in journal (Refereed)
    Abstract [en]

    Schizophrenia and bipolar disorder (BPD) are common neurodevelopmental disorders, characterized by various life-crippling symptoms and high suicide rates. Multiple studies support a strong genetic involvement in the etiology of these disorders, although patterns of inheritance are variable and complex. Adenosine-to-inosine RNA editing is a cellular mechanism, which has been implicated in mental disorders and suicide. To examine the involvement of altered RNA editing in these disorders, we: (i) quantified the mRNA levels of the adenosine deaminase acting on RNA (ADAR) editing enzymes by real-time quantitative polymerase chain reaction, and (ii) measured the editing levels in transcripts of several neuroreceptors using 454 high-throughput sequencing, in dorsolateral-prefrontal cortices of schizophrenics, BPD patients and controls. Increased expression of specific ADAR2 variants with diminished catalytic activity was observed in schizophrenia. Our results also indicate that the I/V editing site in the glutamate receptor, ionotropic kainate 2 (GRIK2) transcript is under-edited in BPD (type I) patients (45.8 versus 53.9%, P = 0.023). GRIK2 has been implicated in mood disorders, and editing of its I/V site can modulate Ca(+2) permeability of the channel, consistent with numerous observations of elevated intracellular Ca(+2) levels in BPD patients. Our findings may therefore, at least partly, explain a molecular mechanism underlying the disorder. In addition, an intriguing correlation was found between editing events on separate exons of GRIK2. Finally, multiple novel editing sites were detected near previously known sites, albeit most with very low editing rates. This supports the hypothesis raised previously regarding the existence of wide-spread low-level 'background' editing as a mechanism that enhances adaptation and evolvability.

  • 16.
    Srinivas, Vivek
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lebrette, Hugo
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Kutin, Yuri
    Sahlin, Margareta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lerche, Michael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Eirich, Jürgen
    Branca, Rui M. M.
    Cox, Nicholas
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Högbom, Martin
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stanford University School of Medicine, USA.
    Metal-free ribonucleotide reduction powered by a DOPA radical in Mycoplasma pathogens2018In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 563, p. 416-420Article in journal (Refereed)
    Abstract [en]

    Ribonucleotide reductase (RNR) catalyses the only known de novo pathway for the production of all four deoxyribonucleotides that are required for DNA synthesis1,2. It is essential for all organisms that use DNA as their genetic material and is a current drug target3,4. Since the discovery that iron is required for function in the aerobic, class I RNR found in all eukaryotes and many bacteria, a dinuclear metal site has been viewed as necessary to generate and stabilize the catalytic radical that is essential for RNR activity5,6,7. Here we describe a group of RNR proteins in Mollicutes—including Mycoplasma pathogens—that possess a metal-independent stable radical residing on a modified tyrosyl residue. Structural, biochemical and spectroscopic characterization reveal a stable 3,4-dihydroxyphenylalanine (DOPA) radical species that directly supports ribonucleotide reduction in vitro and in vivo. This observation overturns the presumed requirement for a dinuclear metal site in aerobic ribonucleotide reductase. The metal-independent radical requires new mechanisms for radical generation and stabilization, processes that are targeted by RNR inhibitors. It is possible that this RNR variant provides an advantage under metal starvation induced by the immune system. Organisms that encode this type of RNR—some of which are developing resistance to antibiotics—are involved in diseases of the respiratory, urinary and genital tracts. Further characterization of this RNR family and its mechanism of cofactor generation will provide insight into new enzymatic chemistry and be of value in devising strategies to combat the pathogens that utilize it. We propose that this RNR subclass is denoted class Ie.

  • 17. Tamas, Ivica
    et al.
    Wernegreen, Jennifer J
    Nystedt, Björn
    Kauppinen, Seth N
    Darby, Alistair C
    Gomaz-Valero, Laura
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Poole, Anthony M
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Andersson, Siv G E
    Endosymbiont gene functions impaired and rescued by polymerase infidelity at poly(A) tracts2008In: PNAS, Vol. 105, no 39, p. 14934-14939Article in journal (Refereed)
  • 18.
    Thureborn, Petter
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics. Södertorn University College, Sweden.
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab). Södertorn University College, Sweden.
    Plathan, Josefin
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
    Poole, Anthony M.
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics. University of Canterbury, New Zealand.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics. Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sjöling, Sara
    A Metagenomics Transect into the Deepest Point of the Baltic Sea Reveals Clear Stratification of Microbial Functional Capacities2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 9, p. e74983-Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is characterized by hyposaline surface waters, hypoxic and anoxic deep waters and sediments. These conditions, which in turn lead to a steep oxygen gradient, are particularly evident at Landsort Deep in the Baltic Proper. Given these substantial differences in environmental parameters at Landsort Deep, we performed a metagenomic census spanning surface to sediment to establish whether the microbial communities at this site are as stratified as the physical environment. We report strong stratification across a depth transect for both functional capacity and taxonomic affiliation, with functional capacity corresponding most closely to key environmental parameters of oxygen, salinity and temperature. We report similarities in functional capacity between the hypoxic community and hadal zone communities, underscoring the substantial degree of eutrophication in the Baltic Proper. Reconstruction of the nitrogen cycle at Landsort deep shows potential for syntrophy between archaeal ammonium oxidizers and bacterial denitrification at anoxic depths, while anaerobic ammonium oxidation genes are absent, despite substantial ammonium levels below the chemocline. Our census also reveals enrichment in genetic prerequisites for a copiotrophic lifestyle and resistance mechanisms reflecting adaptation to prevalent eutrophic conditions and the accumulation of environmental pollutants resulting from ongoing anthropogenic pressures in the Baltic Sea.

  • 19. Zhang, Sicai
    et al.
    Masuyer, Geoffrey
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Zhang, Jie
    Shen, Yi
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Henriksson, Linda
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Miyashita, Shin-Ichiro
    Martinez-Carranza, Markel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Dong, Min
    Stenmark, Pål
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Identification and characterization of a novel botulinum neurotoxin2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 14130Article in journal (Refereed)
    Abstract [en]

    Botulinum neurotoxins are known to have seven serotypes (BoNT/A-G). Here we report a new BoNT serotype, tentatively named BoNT/X, which has the lowest sequence identity with other BoNTs and is not recognized by antisera against known BoNTs. Similar to BoNT/B/D/F/G, BoNT/X cleaves vesicle-associated membrane proteins (VAMP) 1, 2 and 3, but at a novel site (Arg66-Ala67 in VAMP2). Remarkably, BoNT/X is the only toxin that also cleaves non-canonical substrates VAMP4, VAMP5 and Ykt6. To validate its activity, a small amount of full-length BoNT/X was assembled by linking two non-toxic fragments using a transpeptidase (sortase). Assembled BoNT/X cleaves VAMP2 and VAMP4 in cultured neurons and causes flaccid paralysis in mice. Thus, BoNT/X is a novel BoNT with a unique substrate profile. Its discovery posts a challenge to develop effective countermeasures, provides a novel tool for studying intracellular membrane trafficking, and presents a new potential therapeutic toxin for modulating secretions in cells.

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