Role of the transmembrane and extracytoplasmic domain of beta subunits in subunit assembly, intracellular transport, and functional expression of Na,K-pumps.
Open Access
- 15 December 1993
- journal article
- research article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 123 (6), 1751-1759
- https://doi.org/10.1083/jcb.123.6.1751
Abstract
The ubiquitous Na,K- and the gastric H,K-pumps are heterodimeric plasma membrane proteins composed of an alpha and a beta subunit. The H,K-ATPase beta subunit (beta HK) can partially act as a surrogate for the Na,K-ATPase beta subunit (beta NK) in the formation of functional Na,K-pumps (Horisberger et al., 1991. J. Biol. Chem. 257:10338-10343). We have examined the role of the transmembrane and/or the ectodomain of beta NK in (a) its ER retention in the absence of concomitant synthesis of Na,K-ATPase alpha subunits (alpha NK) and (b) the functional expression of Na,K-pumps at the cell surface and their activation by external K+. We have constructed chimeric proteins between Xenopus beta NK and rabbit beta HK by exchanging their NH2-terminal plus transmembrane domain with their COOH-terminal ectodomain (beta NK/HK, beta HK/NK). We have expressed these constructs with or without coexpression of alpha NK in the Xenopus oocyte. In the absence of alpha NK, Xenopus beta NK and all chimera that contained the ectodomain of beta NK were retained in the ER while beta HK and all chimera with the ectodomain of beta HK could leave the ER suggesting that ER retention of unassembled Xenopus beta NK is mediated by a retention signal in the ectodomain. When coexpressed with alpha NK, only beta NK and beta NK/HK chimera assembled efficiently with alpha NK leading to similar high expression of functional Na,K-pumps at the cell surface that exhibited, however, a different apparent K+ affinity. beta HK or chimera with the transmembrane domain of beta HK assembled less efficiently with alpha NK leading to lower expression of functional Na,K-pumps with a different apparent K+ affinity. The data indicate that the transmembrane domain of beta NK is important for efficient assembly with alpha NK and that both the transmembrane and the ectodomain of beta subunits play a role in modulating the transport activity of Na,K-pumps.This publication has 35 references indexed in Scilit:
- Role of Transmembrane Domain Interactions in the Assembly of Class II MHC MoleculesScience, 1992
- Assembly of a hybrid from the α subunit of Na+K+-ATPase and the β subunit of H+K+-ATPaseBiochemical and Biophysical Research Communications, 1992
- The N-terminal domains of acetylcholine receptor subunits contain recognition signals for the initial steps of receptor assemblyCell, 1992
- Peptide-binding specificity of the molecular chaperone BiPNature, 1991
- The functional role of the β‐subunit in the maturation and intracellular transport of Na,K‐ATPaseFEBS Letters, 1991
- A negative slope in the current-voltage relationship of the Na+/K+ pump inXenopus oocytes produced by reduction of external [K+]The Journal of Membrane Biology, 1991
- Mutual dependence of Na,K‐ATPase α‐ and β‐subunits for correct posttranslational processing and intracellular transportFEBS Letters, 1990
- Regulation of Protein Export From the Endoplasmic ReticulumAnnual Review of Cell Biology, 1988
- Structural basis for E1–E2 conformational transitions in Na, K-pump and Ca-pump proteinsThe Journal of Membrane Biology, 1988
- Immunochemical evidence for a transmembrane orientation of both the (sodium(1+), potassium(1+) ion-activated)-ATPase subunitsBiochemistry, 1981