Distinct sensitivities of OmpF and PhoE porins to charged modulators.
The inhibition of the anion-selective PhoE porin by ATP and of the cation-selective OmpF porin by polyamines has been previously documented. In the present study, we have extended the comparison of the inhibitor-porin pairs by investigating the effect of anions (ATP and aspartate) and positively charged polyamines (spermine and cadaverine) on both OmpF and PhoE with the patch-clamp technique, and by comparing directly the gating kinetics of the channels modulated by their respective substrates. The novel findings reported here are (1) that the activity of PhoE is completely unaffected by polyamines, and (2) that the kinetic changes induced by ATP on PhoE or polyamines on OmpF suggest different mechanisms of inhibition. ATP induces a high degree of flickering in the PhoE-mediated current and appears to behave as a blocker of ion flow during its presumed transport through PhoE. Polyamines modulate the kinetics of openings and closings of OmpF, in addition to promoting a blocker-like flickering activity. The strong correlation between sensitivity to inhibitors and ion selectivity suggests that some common molecular determinants are involved in these two properties and is in agreement with the hypothesis that polyamines bind inside the pore of cationic porins.
Department of Biology and Biochemistry, University of Houston, TX 77204-5513, USA.
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D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000838:Anions / Q000378:metabolism / Q000494:pharmacology*; D001224:Aspartic Acid / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002103:Cadaverine / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects; D029968:Escherichia coli Proteins; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D018408:Patch-Clamp Techniques; D011073:Polyamines / Q000378:metabolism / Q000494:pharmacology*; D018272:Porins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013096:Spermine / Q000378:metabolism / Q000494:pharmacology
D000838:Anions; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C109237:OmpF protein; D011073:Polyamines; D018272:Porins; D013096:Spermine; D001224:Aspartic Acid; C082922:PhoE protein, E coli; D000255:Adenosine Triphosphate; D002103:Cadaverine