Probing the energy landscape of the membrane protein bacteriorhodopsin

Harald Janovjak, Jens Struckmeier, Maurice Hubain, Alexej Kedrov, Max Kessler, Daniel J. Müller

Research output: Contribution to journalArticlepeer-review

72 Citations (Scopus)


The folding and stability of transmembrane proteins is a fundamental and unsolved biological problem. Here, single bacteriorhodopsin molecules were mechanically unfolded from native purple membranes using atomic force microscopy and force spectroscopy. The energy landscape of individual transmembrane α helices and polypeptide loops was mapped by monitoring the pulling speed dependence of the unfolding forces and applying Monte Carlo simulations. Single helices formed independently stable units stabilized by a single potential barrier. Mechanical unfolding of the helices was triggered by 3.9-7.7 Å extension, while natural unfolding rates were of the order of 10-3 s-1. Besides acting as individually stable units, helices associated pairwise, establishing a collective potential barrier. The unfolding pathways of individual proteins reflect distinct pulling speed-dependent unfolding routes in their energy landscapes. These observations support the two-stage model of membrane protein folding in which α helices insert into the membrane as stable units and then assemble into the functional protein.

Original languageEnglish
Pages (from-to)871-879
Number of pages9
Issue number5
Publication statusPublished - May 2004
Externally publishedYes


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