title: Janus model of the Na,K-ATPase beta-subunit transmembrane domain: distinct faces mediate alpha/beta assembly and beta-beta homo-oligomerization.
abstract: Na,K-ATPase is a hetero-oligomer of alpha and beta-subunits. The Na,K-ATPase beta-subunit (Na,K-beta) is involved in both the regulation of ion transport activity, and in cell-cell adhesion. By structure prediction and evolutionary analysis, we identified two distinct faces on the Na,K-beta transmembrane domain (TMD) that could mediate protein-protein interactions: a glycine zipper motif and a conserved heptad repeat. Here, we show that the heptad repeat face is involved in the hetero-oligomeric interaction of Na,K-beta with Na,K-alpha, and the glycine zipper face is involved in the homo-oligomerization of Na,K-beta. Point mutations in the heptad repeat motif reduced Na,K-beta binding to Na,K-alpha, and Na,K-ATPase activity. Na,K-beta TMD homo-oligomerized in biological membranes, and mutation of the glycine zipper motif affected oligomerization and cell-cell adhesion. These results provide a structural basis for understanding how Na,K-beta links ion transport and cell-cell adhesion.
authors.affiliation: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California-Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Sonali P
authors.initials: SP
authors.lastname: Barwe
authors.forename: Sanguk
authors.initials: S
authors.lastname: Kim
authors.forename: Sigrid A
authors.initials: SA
authors.lastname: Rajasekaran
authors.forename: James U
authors.initials: JU
authors.lastname: Bowie
authors.forename: Ayyappan K
authors.initials: AK
authors.lastname: Rajasekaran
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002449:Cell Aggregation; D002462:Cell Membrane / Q000201:enzymology; D004285:Dogs; D005998:Glycine / Q000235:genetics; D007930:Leucine / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism*; D020449:Repetitive Sequences, Amino Acid; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D021122:Protein Subunits; D000254:Sodium-Potassium-Exchanging ATPase; D007930:Leucine; D005998:Glycine