Direct single-molecule observation of a protein living in two opposed native structures

Proc Natl Acad Sci U S A. 2009 Jun 23;106(25):10153-8. doi: 10.1073/pnas.0904461106. Epub 2009 Jun 8.


Biological activity in proteins requires them to share the energy landscape for folding and global conformational motions, 2 key determinants of function. Although most structural studies to date have focused on fluctuations around a single structural basin, we directly observe the coexistence of 2 symmetrically opposed conformations for a mutant of the Rop-homodimer (Repressor of Primer) in single-molecule fluorescence resonance energy transfer (smFRET) measurements. We find that mild denaturing conditions can affect the sensitive balance between the conformations, generating an equilibrium ensemble consisting of 2 equally occupied structural basins. Despite the need for large-scale conformational rearrangement, both native structures are dynamically and reversibly adopted for the same paired molecules without separation of the constituent monomers. Such an ability of some proteins or protein complexes to switch between conformations by thermal fluctuations and/or minor environmental changes could be central to their ability to control biological function.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Fluorescence Resonance Energy Transfer / methods*
  • Molecular Sequence Data
  • Mutation
  • Protein Conformation
  • Protein Folding
  • RNA-Binding Proteins / chemistry*
  • RNA-Binding Proteins / genetics


  • Bacterial Proteins
  • RNA-Binding Proteins
  • Rop protein, ColE1 plasmid