title: Unfolding pathways of individual bacteriorhodopsins.
abstract: Atomic force microscopy and single-molecule force spectroscopy were combined to image and manipulate purple membrane patches from Halobacterium salinarum. Individual bacteriorhodopsin molecules were first localized and then extracted from the membrane; the remaining vacancies were imaged again. Anchoring forces between 100 and 200 piconewtons for the different helices were found. Upon extraction, the helices were found to unfold. The force spectra revealed the individuality of the unfolding pathways. Helices G and F as well as helices E and D always unfolded pairwise, whereas helices B and C occasionally unfolded one after the other. Experiments with cleaved loops revealed the origin of the individuality: stabilization of helix B by neighboring helices.
authors.affiliation: CeNS and Lehrstuhl für angewandte Physik, Ludwig Maximilians-Universität München, Amalienstrasse 54, 80799 München, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Oesterhelt
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: M
authors.initials: M
authors.lastname: Pfeiffer
authors.forename: A
authors.initials: A
authors.lastname: Engel
authors.forename: H E
authors.initials: HE
authors.lastname: Gaub
authors.forename: D J
authors.initials: DJ
authors.lastname: Müller
mesh_terms: D000595:Amino Acid Sequence; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D003545:Cysteine / Q000737:chemistry; D019617:Halobacterium salinarum / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D018717:Purple Membrane / Q000737:chemistry*; D012697:Serine Endopeptidases / Q000378:metabolism; D013057:Spectrum Analysis
chemical_list: D008565:Membrane Proteins; D001436:Bacteriorhodopsins; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D003545:Cysteine