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J. Biol. Chem., Vol. 279, Issue 29, 30888-30895, July 16, 2004

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FXYD7, Mapping of Functional Sites Involved in Endoplasmic Reticulum Export, Association With and Regulation of Na,K-ATPase^*

Gilles Crambert, Ciming Li, Lee Kim Swee, and Käthi Geering

From the Institute of Pharmacology and Toxicology of the University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland

The brain-specific FXYD7 is a member of the recently defined FXYD family that associates with the 1-1 Na,K-ATPase isozyme and induces an about 2-fold decrease in its apparent K⁺ affinity. By using the Xenopus oocyte as an expression system, we have investigated the role of conserved and FXYD7-specific amino acids in the cellular routing of FXYD7 and in its association with and regulation of Na,K-ATPase. In contrast to FXYD2 and FXYD4, the studies on FXYD7 show that the conserved FXYD motif in the extracytoplasmic domain is not involved in the efficient association of FXYD7 with Na,K-ATPase. On the other hand, the conserved Gly⁴⁰ and Gly²⁹, located on the same face of the transmembrane helix, were found to be implicated both in the association with and the regulation of Na,K-ATPase. Mutational analysis of FXYD7-specific regions revealed the presence of an ER export signal at the end of the cytoplasmic tail. Deletion of a C-terminal valine residue in FXYD7 significantly delayed and decreased its O-glycosylation processing and retarded the rate of its cell surface expression. This result indicates that the C-terminal valine residue is involved in the rapid and selective ER export of FXYD7, which could explain the observed post-translational association of FXYD7 with Na,K-ATPase. In conclusion, our study on FXYD7 provides new information on structural determinants of general importance for FXYD protein action. Moreover, FXYD7 is identified as a new member of proteins with a regulated ER export, which suggests that, among FXYD proteins, FXYD7 has a particular regulatory function in brain.

Received for publication, December 10, 2003 , and in revised form, May 6, 2004.

^* This study was supported by Grant No. 31-64793.01 (to K. G.) from the Swiss National Science Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 41-21-692-54-10; Fax: 41-21-692-53-55; E-mail: kaethi.geering{at}ipharm.unil.ch.

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