title: Interaction of cephalosporins with outer membrane channels of Escherichia coli. Revealing binding by fluorescence quenching and ion conductance fluctuations.
abstract: Outer membrane channels in gram-negative bacteria are implicated in the influx of the latest generation of cephalosporins. We have measured the interaction strengths of ceftriaxone, cefpirome and ceftazidime in the two most abundant outer membrane porins of Escherichia coli, OmpF and OmpC, by both ion current fluctuations through single protein channels and fluorescence quenching. Statistical analysis of individual antibiotic entry events in membrane-incorporated porins yielded the kinetic rates and the equilibrium binding constant of each antibiotic-porin pair. Affinity constants were independently obtained by measuring the static quenching of inherent tryptophan fluorescence in the porins in the presence of the antibiotics. Through an empirical inner filter effect correction we have succeeded in measuring the chemical interaction of these strongly absorbing antibiotics, and obtained a qualitative agreement with conductance measurements. The interaction of all three antibiotics is smaller for OmpC than OmpF, and in the case of each porin the interaction strength series ceftriaxone > cefpirome > ceftazidime is maintained.
authors.affiliation: Requimte, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal.
authors.forename: Marcos
authors.initials: M
authors.lastname: Lovelle
authors.forename: Tivadar
authors.initials: T
authors.lastname: Mach
authors.forename: Kozhinjampara R
authors.initials: KR
authors.lastname: Mahendran
authors.forename: Helge
authors.initials: H
authors.lastname: Weingart
authors.forename: Mathias
authors.initials: M
authors.lastname: Winterhalter
authors.forename: Paula
authors.initials: P
authors.lastname: Gameiro
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D002511:Cephalosporins / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology*; D007477:Ions / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D018272:Porins / Q000737:chemistry / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D013050:Spectrometry, Fluorescence
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D007477:Ions; C113724:OmpC protein; C109237:OmpF protein; D018272:Porins