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Tangled up in knots: structures of inactivated forms of E. coli class Ia ribonucleotide reductase

Christina M Zimanyi1, Nozomi Ando, Edward J Brignole

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Structure (London, England : 1993)
|June 26, 2012
PubMed

Insights

Ribonucleotide reductases (RNRs) form unusual interlocking rings when inhibited by dATP or gemcitabine. These structures, revealed by X-ray crystallography, offer new insights into DNA synthesis regulation.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Molecular Biology

Background:

  • Ribonucleotide reductases (RNRs) are crucial enzymes for DNA synthesis and repair.
  • RNRs are validated targets for anticancer drugs like gemcitabine.
  • Previous studies showed dATP induces E. coli class Ia RNR subunits to form α4β4 rings.

Purpose of the Study:

  • To determine the X-ray structure of gemcitabine-inhibited E. coli RNR.
  • To investigate the formation of megacomplexes and catenated structures in RNRs.
  • To elucidate the mechanism behind the formation of these unusual RNR assemblies.

Main Methods:

  • X-ray crystallography of E. coli RNR.
  • Small-angle X-ray scattering (SAXS).
  • Electron microscopy (EM).

Main Results:

  • The first X-ray structure of gemcitabine-inhibited E. coli RNR was determined.
  • α4β4 rings were observed to interlock, forming an (α4β4)2 megacomplex.
  • A distinct crystal lattice was observed for the dATP-inhibited RNR structure compared to the gemcitabine-inhibited structure.
  • SAXS and EM data provided insights into concatenation mechanisms.

Conclusions:

  • Gemcitabine and dATP induce the formation of unprecedented (α4β4)2 megacomplexes in E. coli RNR.
  • These studies reveal novel mechanisms for RNR inhibition and regulation.
  • Understanding these structures may inform the development of new anticancer therapies targeting RNR.

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