Download MendeleyClass Id ribonucleotide reductase utilizes a Mn2(IV,III) cofactor and undergoes large conformational changes on metal loading.
Rozman Grinberg, I., Berglund, S., Hasan, M., Lundin, D., Ho, F.M., Magnuson, A., Logan, D.T., Sjoberg, B.M., Berggren, G.(2019) J Biol Inorg Chem 24: 863-877
- PubMed: 31414238
- DOI: https://doi.org/10.1007/s00775-019-01697-8
- Primary Citation of Related Structures:
6SF4, 6SF5 - PubMed Abstract:
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. H 2 O 2 and superoxide (O 2 ·- ). Considering the observed differences in the efficiency of these two activating reagents, we propose that the physiologically relevant mechanism involves superoxide.
Organizational Affiliation:
Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
