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Borrowed subunit makes ion pump fold

P2-type ATPases such as the plasma membrane Na⁺/K⁺-ATPase, the gastric H⁺/K⁺-ATPase and the sarcoplasmic reticulum Ca²⁺-ATPase are transmembrane proteins that pump metal ions across membranes. The Na⁺/K⁺-ATPase and H⁺/K⁺-ATPase each comprise a catalytic subunit and a ß subunit that is essential for correct folding. The Ca²⁺-ATPase has an subunit but – despite having a topology and overall hydropathy similar to its relatives – seems to get by without a ß subunit. So how can it fold correctly? Masaru Kawamura and co-workers show that it can borrow ß subunits from its relatives (see p. 1875). They find that the Ca²⁺-ATPase can be coimmunoprecipitated with the ß-subunits of the Na⁺/K⁺-ATPase and H⁺/K⁺-ATPase in oocytes during the early stages of its biogenesis. Using pulse-chase experiments, they then demonstrate that the association is transient and that the ß-subunits dissociate as they mature and become fully glycosylated. One function of the ß subunits is to ensure correct packing of Na⁺/K⁺-ATPase and H⁺/K⁺-ATPase subunits by associating with a conserved SYGQ sequence between transmembrane segments seven and eight. The Ca²⁺-ATPase lacks this sequence, which might explain why it associates with ß subunits only transiently.

Related articles in JCS:

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

Shunsuke Noguchi, Nobuhito Sone, and Masaru Kawamura
JCS 2003 116: 1875-1880. [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JCS Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content