Free energy of membrane protein unfolding derived from single-molecule force measurements

Johannes Preiner, Harald Janovjak, Christian Rankl, Helene Knaus, David A. Cisneros, Alexej Kedrov, Ferry Kienberger, Daniel J. Muller, Peter Hinterdorfer

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)


Mechanical single-molecule techniques offer exciting possibilities to investigate protein folding and stability in native environments at submolecular resolution. By applying a free-energy reconstruction procedure developed by Hummer and Szabo, which is based on a statistical theorem introduced by Jarzynski, we determined the unfolding free energy of the membrane proteins bacteriorhodopsin (BR), halorhodopsin, and the sodium-proton antiporter NhaA. The calculated energies ranged from 290.5 kcal/mol for BR to 485.5 kcal/mol for NhaA. For the remarkably stable BR, the equilibrium unfolding free energy was independent of pulling rate and temperature ranging between 18 and 42°C. Our experiments also revealed heterogeneous energetic properties in individual transmembrane helices. In halorhodopsin, the stabilization of a short helical segment yielded a characteristic signature in the energy profile. In NhaA, a pronounced peak was observed at a functionally important site in the protein. Since a large variety of single- and multispan membrane proteins can be tackled in mechanical unfolding experiments, our approach provides a basis for systematically elucidating energetic properties of membrane proteins with the resolution of individual secondary-structure elements.

Original languageEnglish
Pages (from-to)930-937
Number of pages8
JournalBiophysical Journal
Issue number3
Publication statusPublished - 1 Aug 2007


  • Bacteriorhodopsins/chemistry
  • Drug Stability
  • Kinetics
  • Membrane Proteins/chemistry
  • Models, Molecular
  • Protein Denaturation
  • Protein Folding
  • Thermodynamics


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