title: Voltage sensing in the PhoE and OmpF outer membrane porins of Escherichia coli: role of charged residues.
abstract: The porins PhoE and OmpF form anion and cation-selective pores, respectively, in the outer membrane of Escherichia coli. Each monomer of these trimeric proteins consists of a 16-stranded beta-barrel, which contains a constriction at half the height of the channel. The functional significance of a transverse electrical field that is formed by charged amino acid residues within the constriction zone was investigated. For this purpose, the PhoE residues R37, R75, K18 and E110 were substituted by neutral amino acids. The mutant pores allowed an increased permeation of beta-lactam antibiotics across the outer membrane in vivo, although the single channel conductance, measured in planar lipid bilayers, was not increased or even slightly decreased. Replacement of the positively charged residues resulted in a decreased voltage sensitivity, whereas the substitution of a negatively charged residue resulted in an increased voltage sensitivity. Similar substitutions in OmpF caused the opposite effects, i.e. the substitution of positive and negative charges resulted in increased and decreased voltage sensitivity, respectively. Together, the results suggest that opposite charges, i.e. positive charges in anion-selective and negative charges in cation-selective porins, act as sensors for voltage gating.
authors.affiliation: Department of Molecular Cell Biology and Institute of Biomembranes, Utrecht University, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Van Gelder
authors.forename: N
authors.initials: N
authors.lastname: Saint
authors.forename: P
authors.initials: P
authors.lastname: Phale
authors.forename: E F
authors.initials: EF
authors.lastname: Eppens
authors.forename: A
authors.initials: A
authors.lastname: Prilipov
authors.forename: R
authors.initials: R
authors.lastname: van Boxtel
authors.forename: J P
authors.initials: JP
authors.lastname: Rosenbusch
authors.forename: J
authors.initials: J
authors.lastname: Tommassen
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology*; D002463:Cell Membrane Permeability; D004594:Electrophysiology; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D015640:Ion Channel Gating; D016296:Mutagenesis; D018272:Porins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D018272:Porins; C082922:PhoE protein, E coli