X in

β-subunit. In some tissues, like the kidney, however, a third non-obligatory subunit is present. In 1978 Forbush et al. [1] FXYD2 is expressed in the nephron. Although its exact localization has been the subject of various studies, the results seem to be somewhat at variance [3–5]. Recent research, how-ever, indicates different distribution patterns for the two splice Available online at www.sciencedirect.com 17identified this small polypeptide that could be labeled with an ouabain derivate and that directly associated with Na,K-Autosomal dominant renal hypomagnesemia, associated with hypocalciurea, has been linked to a G to A mutation at nucleotide position 121 in the FXYD2 gene, resulting in the substitution of Gly with Arg at residue 41 of the protein. FXYD2, also called the Na,K-ATPase γ-subunit, binds to Na,K-ATPase and influences its cation affinities. In this paper, we provide evidence for the molecular mechanism underlying the dominant character of the disorder. Co-immunoprecipitation experiments using tagged FXYD2 proteins demonstrated that wild type FXYD2 proteins oligomerise. Moreover, FXYD2-G41R also shows oligomerisation with itself and with the wild type protein. In the case of FXYD2-G41R, however, formation of homo-oligomers was prevented by addition of DTT or introduction of the C52A mutation. Finally, we demonstrated that artificial glycosylation of the wild type FXYD2 is reduced when co-expressed with FXYD2-G41R. These data indicate that binding of FXYD2-G41R to wild type FXYD2 subunit might abrogate the routing of wild type FXYD2 to the plasma membrane thus causing the dominant nature of this mutation