Disease causing mutations affect ENaC gating

Abstract

Gain and loss‐of‐function mutations in the epithelial Na channel (ENaC) affect renal Na+ excretion. Here, we identify five mutations in ENaC that lead to changes in single channel properties, and should be informative about structure‐function relations within the channel protein. Channels containing the PHA‐I mutation, G37S in β‐ENaC, are voltage‐dependent where Po is low at physiological potentials. This critical Gly is in a conserved HG motif in the cytosolic NH2‐terminus key to gating. Another PHA‐I mutation, the KYS106‐108‐>N substitution in γ‐ENaC, also markedly decreases current by decreasing Po in a voltage‐dependent manner. The PHA‐I mutation, S562P in γ‐ENaC, results in complete loss of function. S562 occupies a critical position in the selectivity filter of the channel pore possibly being involved in coordination of the conductive ion during permeation. The N530S Liddle's mutation in the γ‐subunit of ENaC replaces a conserved (in ENaC) Arg within the extracellular vestibule of the pore one position downstream of the Deg site. Channels containing γ‐ENaC harboring the N530S substitution have increased Po. The Liddle's mutation W493R in α‐ENaC increases channel activity and Po. W493 also is located in extracellular mouth of the pore and is believed to interact in an electrostatic manner with the key pore residue R492. Notabely, none of these mutations affected single channel conductance.