title: Allosteric inhibition of the epithelial Na+ channel through peptide binding at peripheral finger and thumb domains.
abstract: The epithelial Na(+) channel (ENaC) mediates the rate-limiting step in transepithelial Na(+) transport in the distal segments of the nephron and in the lung. ENaC subunits are cleaved by proteases, resulting in channel activation due to the release of inhibitory tracts. Peptides derived from these tracts inhibit channel activity. The mechanism by which these intrinsic inhibitory tracts reduce channel activity is unknown, as are the sites where these tracts interact with other residues within the channel. We performed site-directed mutagenesis in large portions of the predicted periphery of the extracellular region of the α subunit and measured the effect of mutations on an 8-residue inhibitory tract-derived peptide. Our data show that the inhibitory peptide likely binds to specific residues within the finger and thumb domains of ENaC. Pairwise interactions between the peptide and the channel were identified by double mutant cycle experiments. Our data suggest that the inhibitory peptide has a specific peptide orientation within its binding site. Extended to the intrinsic inhibitory tract, our data suggest that proteases activate ENaC by removing residues that bind at the finger-thumb domain interface.
authors.affiliation: Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Ossama B
authors.initials: OB
authors.lastname: Kashlan
authors.forename: Cary R
authors.initials: CR
authors.lastname: Boyd
authors.forename: Christos
authors.initials: C
authors.lastname: Argyropoulos
authors.forename: Sora
authors.initials: S
authors.lastname: Okumura
authors.forename: Rebecca P
authors.initials: RP
authors.lastname: Hughey
authors.forename: Michael
authors.initials: M
authors.lastname: Grabe
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Kleyman
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D010455:Peptides / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; D010455:Peptides; D021122:Protein Subunits
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