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  • 1.
    Rozman Grinberg, Inna
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Berglund, Sigrid
    Hasan, Mahmudul
    Lundin, Daniel
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Ho, Felix M.
    Magnuson, Ann
    Logan, Derek T.
    Sjöberg, Britt-Marie
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Berggren, Gustav
    Class Id ribonucleotide reductase utilizes a Mn-2(IV,III) cofactor and undergoes large conformational changes on metal loading2019In: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 24, no 6, p. 863-877Article in journal (Refereed)
    Abstract [en]

    Outside of the photosynthetic machinery, high-valent manganese cofactors are rare in biology. It was proposed that a recently discovered subclass of ribonucleotide reductase (RNR), class Id, is dependent on a Mn-2(IV,III) cofactor for catalysis. Class I RNRs consist of a substrate-binding component (NrdA) and a metal-containing radical-generating component (NrdB). Herein we utilize a combination of EPR spectroscopy and enzyme assays to underscore the enzymatic relevance of the Mn-2(IV,III) cofactor in class Id NrdB from Facklamia ignava. Once formed, the Mn-2(IV,III) cofactor confers enzyme activity that correlates well with cofactor quantity. Moreover, we present the X-ray structure of the apo- and aerobically Mn-loaded forms of the homologous class Id NrdB from Leeuwenhoekiella blandensis, revealing a dimanganese centre typical of the subclass, with a tyrosine residue maintained at distance from the metal centre and a lysine residue projected towards the metals. Structural comparison of the apo- and metal-loaded forms of the protein reveals a refolding of the loop containing the conserved lysine and an unusual shift in the orientation of helices within a monomer, leading to the opening of a channel towards the metal site. Such major conformational changes have not been observed in NrdB proteins before. Finally, in vitro reconstitution experiments reveal that the high-valent manganese cofactor is not formed spontaneously from oxygen, but can be generated from at least two different reduced oxygen species, i.e. H2O2 and superoxide (O2 center dot-). Considering the observed differences in the efficiency of these two activating reagents, we propose that the physiologically relevant mechanism involves superoxide.

  • 2.
    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.

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