Outer membrane protein K of Escherichia coli: Purification and pore-forming properties in lipid bilayer membranes

C. Whitfield, Robert Hancock, J. W. Costerton

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Protein K, a recently described outer membrane protein correlated with encapsulation in Escherichia coli (Paakkanen et al., J. Bacteriol. 138:835-841, 1979), has been purified to apparent homogeneity. Purification was based upon the noncovalent association of protein K with peptidoglycan, and the purified protein was shown to form sodium dodecyl sulfate-resistant oligomers on polyacrylamide gels. Incorporation of small amounts (10-10 to 10-11 M) of purified protein K into artificial lipid bilayers resulted in an increase, by many orders of magnitude, in membrane conductance. The increased conductance resulted from the formation of large, water-filled, ion-permeable channel exhibiting single-channel conductance in 1.0 M KCl of 1.83 nS. The membrane conductance showed a linear relationship between current and applied voltage and was not voltage induced or regulated. The channel was permeable to large organic ions (e.g., Tris+ Cl-) and, based upon a pore length of 7.5 nm, a minimum channel diameter of 1.2 nm was estimated; these properties resemble values for other enteric porins. The possible biological role of the pores produced by protein K is discussed.

Original languageEnglish
Pages (from-to)873-879
Number of pages7
JournalJournal of bacteriology
Issue number2
Publication statusPublished - 1 Dec 1983
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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