Mutual dependence of Na,K‐ATPase α‐ and β‐subunits for correct posttranslational processing and intracellular transport

Abstract

In this study, we have followed the fate of newly synthesized cc-and B-subunits of Na,K-ATPase in Xenopus oocytes injected with a and/or B cRNA to examine whether assembly of the two subunits is needed for a correct folding and/or for intracellular transport of Na,K-ATPase. Our data indicate that (1) assembly of a-and /?-subunits occurs at the level of the ER, (2) p-subunits are needed for the newly synthesized a-subunit to adopt a stable configuration and (3) a-and B-subunits mutually depend on each other to be transported out of the ER.

Endoplasmic Reticulum Quality Control of Oligomeric Membrane Proteins: Topogenic Determinants Involved in the Degradation of the Unassembled Na,K-ATPase α Subunit and in Its Stabilization by β Subunit Assembly

“…To study the degradation of ␣ variants, oocytes were metabolically labeled at 19°C for 6 or 24 h in modified Barth's medium containing 0.6 mCi/ml [ 35 S]methionine (New England Nuclear, Boston, MA) and subjected to a chase period of 24 and/or 48 h in modified Barth's medium containing 10 mM unlabeled methionine. Digitonin extracts were prepared after the pulse and chase period and subjected to immunoprecipitation under denaturing or nondenaturing conditions as previously described (Jaunin et al, 1993) by using polyclonal anti-␣ or anti-␤ antibodies (Ackermann and Geering, 1990). To distinguish glycosylated from nonglycosylated species of ␣-␤ chimera, immunoprecipitated samples were subjected to endoglycosidase H (Endo H; Calbiochem-Novabiochem, La Jolla, CA) treatment as described (Jaunin et al, 1993).…”

Regulation of Na+/K+-ATPase by Nuclear Respiratory Factor 1

“…38 and 39). The association of the ␤-subunit facilitates the correct membrane integration and packing of the ␣-subunit, which is necessary for its protection against cellular degradation (40), for its acquisition of functional properties (41), and for its routing to the plasma membrane (42). In tissues, including the brain, the activity of the Na ϩ /K ϩ -ATPase enzyme correlates with the level of ␤1 mRNA content (43).…”

Transient association of the sarcoplasmic reticulum Ca2+ATPase with the Na+/K+-ATPase and H+/K+-ATPase β-subunits during its biogenesis in Xenopus oocytes

“…Although this association occurred in oocytes under the artificial experimental condition we used, the association seems to suggest some physiological role for the β-subunit in the course of the biogenesis of the SR Ca 2+ ATPase. One of the roles of the β-subunit in the Na + /K + ATPase is to assist the correct packing of the nascent α-subunit in membranes (Noguchi et al, 1987;Horowitz et al, 1990;Ackermann and Geering, 1990;Klaassen et al, 1993) through the association with the conserved amino acids (SYGQ) in the extracellular loop between M7 and M8 of the α-subunit (Colonna et al, 1997). Because the SR Ca 2+ ATPase and the Na + /K + ATPase α-subunits have similar membrane topologies, it is plausible that the α-subunits of not only the Na + /K + ATPase but also the SR Ca 2+ ATPase are assisted by association with the β-subunit for correct packing into membranes.…”