MUTATION OF A CONSERVED PROLINE RESIDUE IN THE BETA-SUBUNIT ECTODOMAIN PREVENTS NA+-K+-ATPASE OLIGOMERIZATION

A highly conserved sequence motif (4 tyrosines and 1 proline: YYPYY) of the Na+-K+-adenosinetriphosphatase (ATPase) beta1-subunit ectodomain has been mutagenized to study its possible role in alpha/beta-assembly and sodium pump function. Single as well as double tyrosine mutants (tyrosine to phenylalanine: Y to F) of Xenopus laevis beta1-subunits are able to associate with alpha1-subunits and form functional Na-K pumps at the plasma membrane that are indistinguishable from wild-type alpha1,beta1-Na-K pumps (as assessed by measurements of ouabain binding, Rb-86 flux, Na-K pump current, and activation by external potassium). In contrast, a single proline mutation (proline to glycine: P244G) reduced by >90% the proper assembly and function of Na+-K+-ATPase, despite a normal rate of synthesis and core glycosylation. Our data indicate that proline-244 plays a critical role in the proper folding of the beta-subunit and its ability to associate efficiently with the alpha1-subunit in the endoplasmic reticulum.