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

Author(s): Preiner, Johannes; Janovjak, Harald; Rankl, Christian; Knaus, Helene; Cisneros, David A; Kedrov, Alexej; Kienberger, Ferry; Mueller, Daniel J; Hinterdorfer, Peter
Article Title: Free energy of membrane protein unfolding derived from single-molecule force measurements
Abstract: 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 290.5kcal/mol for BR to 485.5kcal/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.
Journal Title: Biophysical Journal
Volume: 93
Issue 3
ISSN: 1542-0086
Publisher: Biophysical Society  
Date Published: 2007-08-01
Start Page: 930
End Page: 937
DOI: 10.1529/biophysj.106.096982
Open access: yes (repository)