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Olivia M Peduzzi1, Gavin M Palowitch2,3, John P Gajewski1

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This summary is machine-generated.

Ribonucleotide reductases (RNRs) are vital for DNA synthesis. The Francisella hispaniensis RNR beta subunit contains a unique iron cofactor and tyrosyl radical, showing unusual structural and functional adaptations.

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Area of Science:

  • Biochemistry and Molecular Biology
  • Enzymology
  • Structural Biology

Background:

  • Ribonucleotide reductases (RNRs) are essential enzymes for DNA biosynthesis, catalyzing the production of 2'-deoxynucleotides.
  • Class I RNRs utilize a β subunit to generate a crucial thiyl radical in the α subunit, initiating the catalytic cycle.
  • The oxidant in the β subunit can be a tyrosyl radical (Y•), a dimetal cluster, or a dihydroxylphenylalanine (DOPA) radical, with metal dependence varying across RNR classes.

Purpose of the Study:

  • To characterize the structure and function of the β subunit from *Francisella hispaniensis* (Fh) RNR, an enzyme from an uncharacterized sequence cluster found in human pathogens.
  • To investigate the nature of the cofactor and unusual structural features of *Fh* β and their potential implications for the bacterium's survival.

Main Methods:

  • Structural analysis of the apo form of *Fh* β.
  • Biochemical assays to determine cofactor composition (Fe2(III/III)/Y•).
  • Enzyme kinetics and radical stability studies, including hydroxyurea sensitivity assays during turnover with the α subunit.

Main Results:

  • The *Fh* β subunit harbors a Fe2(III/III)/Y• cofactor, similar to eukaryotic and *E. coli* class Ia RNRs.
  • Unusual structural features were observed, including an unwound helix in the apo form and a repositioned tyrosyl radical.
  • The tyrosyl radical in resting *Fh* β is highly resistant to reduction but becomes significantly more sensitive during catalytic turnover with the α subunit.

Conclusions:

  • The *Fh* RNR β subunit possesses unique structural and functional properties, including a conserved aromatic residue (W194) near W37, potentially involved in α-Cys oxidation.
  • The radical's modulated sensitivity to reduction suggests an adaptation to evade host redox defenses targeting the pathogen's essential RNR.
  • These findings provide insights into the evolutionary adaptations of RNRs in pathogenic bacteria and their interaction with host environments.