title: 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 (α, β, and γ); 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 α-, β- and γ-subunits. We show that for α-, β- and γ-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 αβγ-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.
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Stewart
authors.forename: Silke
authors.initials: S
authors.lastname: Haerteis
authors.forename: Alexei
authors.initials: A
authors.lastname: Diakov
authors.forename: Christoph
authors.initials: C
authors.lastname: Korbmacher
authors.forename: J Michael
authors.initials: JM
authors.lastname: Edwardson
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D053503:Epithelial Sodium Channels / Q000737:chemistry* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry; D018625:Microscopy, Atomic Force; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D007140:Immunoglobulin Fab Fragments; D021122:Protein Subunits