K. Geering et al., MUTATION OF A CONSERVED PROLINE RESIDUE IN THE BETA-SUBUNIT ECTODOMAIN PREVENTS NA-K+-ATPASE OLIGOMERIZATION(), The American journal of physiology, 265(4), 1993, pp. 30001169-30001174
A highly conserved sequence motif (4 tyrosines and 1 proline: YYPYY) o
f the Na+-K+-adenosinetriphosphatase (ATPase) beta1-subunit ectodomain
has been mutagenized to study its possible role in alpha/beta-assembl
y and sodium pump function. Single as well as double tyrosine mutants
(tyrosine to phenylalanine: Y to F) of Xenopus laevis beta1-subunits a
re able to associate with alpha1-subunits and form functional Na-K pum
ps at the plasma membrane that are indistinguishable from wild-type al
pha1,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) re
duced by >90% the proper assembly and function of Na+-K+-ATPase, despi
te a normal rate of synthesis and core glycosylation. Our data indicat
e 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.