Second mutations rescue point mutant of the Na+/H+ exchanger NHE1 showing defective surface expression

We studied the effect of point mutation within the putative 11th transmembr ane domain (TM11) of the Na+/H+ exchanger NHE1 on the plasma membrane expre ssion. Of the 19 mutants tested, two mutants (Tyr454 or Arg458 replaced by Cys) were retained in the endoplasmic reticulum, Interestingly, Y454C was e xpressed on the cell surface when one of the endogenous cysteine residues a t position 8, 133, 421, or 477 was substituted with alanine. Random mutagen esis at Cys8 and its surrounding residues in the cytosolic N-tail revealed that replacement of Cys8 with Ala,vas the only identified single residue mu tation that rescued Y454C, These results suggest that the abnormal conforma tion of the region of TM11 containing the Y454C mutation is compensated by the second mutation within other domains such as the IV-tail, This approach may provide evidence for the interdomain interaction in NHE1. (C) 2000 Fed eration of European Biochemical Societies, Published by Elsevier Science B. V. All rights reserved.