Stabilization in microsomal membranes of the fifth transmembrane segment of the Na+,K(+)-ATPase alpha subunit with proline to leucine mutation.

Abstract

We have reported that the fifth transmembrane segment of the Na+,K(+)-ATPase alpha subunit could not be inserted into microsomal membranes when it was synthesized from the truncated alpha 1 cDNA. In this study, three proline residues in the segment were changed into leucine residues by site-directed mutagenesis. Replacement of all three proline residues by leucine residues allowed the insertion of this segment and its translocation. This result confirms our previous finding and demonstrates that three proline residues in the fifth transmembrane segment prevent insertion of the segment into the membrane.