Functional Roles of Clusters of Hydrophobic and Polar Residues in the Epithelial Na+ Channel Knuckle Domain.
J Biol Chem
; 290(41): 25140-50, 2015 Oct 09.
Article
em En
| MEDLINE
| ID: mdl-26306034
ABSTRACT
The extracellular regions of epithelial Na(+) channel subunits are highly ordered structures composed of domains formed by α helices and ß strands. Deletion of the peripheral knuckle domain of the α subunit in the αßγ trimer results in channel activation, reflecting an increase in channel open probability due to a loss of the inhibitory effect of external Na(+) (Na(+) self-inhibition). In contrast, deletion of either the ß or γ subunit knuckle domain within the αßγ trimer dramatically reduces epithelial Na(+) channel function and surface expression, and impairs subunit maturation. We systematically mutated individual α subunit knuckle domain residues and assessed functional properties of these mutants. Cysteine substitutions at 14 of 28 residues significantly suppressed Na(+) self-inhibition. The side chains of a cluster of these residues are non-polar and are predicted to be directed toward the palm domain, whereas a group of polar residues are predicted to orient their side chains toward the space between the knuckle and finger domains. Among the mutants causing the greatest suppression of Na(+) self-inhibition were αP521C, αI529C, and αS534C. The introduction of Cys residues at homologous sites within either the ß or γ subunit knuckle domain resulted in little or no change in Na(+) self-inhibition. Our results suggest that multiple residues in the α subunit knuckle domain contribute to the mechanism of Na(+) self-inhibition by interacting with palm and finger domain residues via two separate and chemically distinct motifs.
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Base de dados:
MEDLINE
Assunto principal:
Canais Epiteliais de Sódio
/
Interações Hidrofóbicas e Hidrofílicas
Tipo de estudo:
Prognostic_studies
Limite:
Animals
/
Humans
Idioma:
En
Revista:
J Biol Chem
Ano de publicação:
2015
Tipo de documento:
Article