Atomic force microscopy reveals the architecture of the epithelial sodium channel (ENaC).

ABSTRACT: The epithelial sodium channel (ENaC) is a member of the ENaC/degenerin superfamily. ENaC is a heteromultimer containing three homologous subunits (?, ?, and ?); however, the subunit stoichiometry is still controversial. Here, we addressed this issue using atomic force microscopy imaging of complexes between isolated ENaC and antibodies/Fab fragments directed against specific epitope tags on the ?-, ?- and ?-subunits. We show that for ?-, ?- and ?-ENaC alone, pairs of antibodies decorate the channel at an angle of 120°, indicating that the individual subunits assemble as homotrimers. A similar approach demonstrates that ???-ENaC assembles as a heterotrimer containing one copy of each subunit. Intriguingly, all four subunit combinations also produce higher-order structures containing two or three individual trimers. The trimer-of-trimers organization would account for earlier reports that ENaC contains eight to nine subunits.

SUBMITTER: Stewart AP 

PROVIDER: S-EPMC3173231 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature