title: Probing the energy landscape of the membrane protein bacteriorhodopsin.
abstract: 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 alpha 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 A 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 alpha helices insert into the membrane as stable units and then assemble into the functional protein.
authors.affiliation: BIOTEC, University of Technology Dresden, 01307 Dresden, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Janovjak
authors.forename: Jens
authors.initials: J
authors.lastname: Struckmeier
authors.forename: Maurice
authors.initials: M
authors.lastname: Hubain
authors.forename: Alexej
authors.initials: A
authors.lastname: Kedrov
authors.forename: Max
authors.initials: M
authors.lastname: Kessler
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Müller
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D019617:Halobacterium salinarum / Q000737:chemistry / Q000378:metabolism; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D013057:Spectrum Analysis
chemical_list: D001436:Bacteriorhodopsins