title: Observing a lipid-dependent alteration in single lactose permeases.
abstract: Lipids of the Escherichia coli membrane are mainly composed of 70%-80% phosphatidylethanolamine (PE) and 20%-25% phosphatidylglycerol (PG). Biochemical studies indicate that the depletion of PE causes inversion of the N-terminal helix bundle of the lactose permease (LacY), and helix VII becomes extramembranous. Here we study this phenomenon using single-molecule force spectroscopy, which is sensitive to the structure of membrane proteins. In PE and PG at a ratio of 3:1, ∼95% of the LacY molecules adopt a native structure. However, when PE is omitted and the membrane contains PG only, LacY almost equally populates a native and a perturbed conformation. The most drastic changes occur at helices VI and VII and the intervening loop. Since helix VII contains Asp237 and Asp240, zwitterionic PE may suppress electrostatic repulsion between LacY and PG in the PE:PG environment. Thus, PE promotes a native fold and prevents LacY from populating a functionally defective, nonnative conformation.
authors: Department of Biosystems Science and Engineering, ETH Zurich, 4058 Basel, Switzerland.
authors: Tetiana
authors: T
authors: Serdiuk
authors: Department of Physiology, University of California, Los Angeles, CA 90095, USA.
authors: Junichi
authors: J
authors: Sugihara
authors: Department of Biosystems Science and Engineering, ETH Zurich, 4058 Basel, Switzerland.
authors: Stefania A
authors: SA
authors: Mari
authors: Department of Physiology, University of California, Los Angeles, CA 90095, USA; Department of Microbiology, Immunology & Molecular Genetics, University of California, Los Angeles, CA 90095, USA; Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA. Electronic address: rkaback@mednet.ucla.edu.
authors: H Ronald
authors: HR
authors: Kaback
authors: Department of Biosystems Science and Engineering, ETH Zurich, 4058 Basel, Switzerland. Electronic address: daniel.mueller@bsse.ethz.ch.
authors: Daniel J
authors: DJ
authors: Müller
mesh_terms: D000595:Amino Acid Sequence; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D027981:Symporters / Q000737:chemistry* / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008563:Membrane Lipids; D009004:Monosaccharide Transport Proteins; D027981:Symporters