Resolution of Stepwise Cooperativities of Copper Binding by the Homotetrameric Copper-Sensitive Operon Repressor (CsoR): Impact on Structure and Stability

Angew Chem Int Ed Engl. 2015 Oct 19;54(43):12795-9. doi: 10.1002/anie.201506349. Epub 2015 Sep 2.


The cooperativity of ligand binding is central to biological regulation and new approaches are needed to quantify these allosteric relationships. Herein, we exploit a suite of mass spectrometry (MS) experiments to provide novel insights into homotropic Cu-binding cooperativity, gas-phase stabilities and conformational ensembles of the D2 -symmetric, homotetrameric copper-sensitive operon repressor (CsoR) as a function of Cu(I) ligation state. Cu(I) binding is overall positively cooperative, but is characterized by distinct ligation state-specific cooperativities. Structural transitions occur upon binding the first and fourth Cu(I) , with the latter occurring with significantly higher cooperativity than previous steps; this results in the formation of a holo-tetramer that is markedly more resistant than apo-, and partially ligated CsoR tetramers toward surface-induced dissociation (SID).

Keywords: allostery; copper; metalloproteins; metalloregulation; surface-induced dissociation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Copper / metabolism*
  • Geobacillus / chemistry
  • Geobacillus / metabolism*
  • Models, Molecular
  • Operon
  • Protein Conformation
  • Protein Multimerization
  • Protein Stability
  • Repressor Proteins / chemistry
  • Repressor Proteins / metabolism*


  • Repressor Proteins
  • Copper