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Dimerization is necessary for the physiological activity of Na + /H + Exchanger NHE1
Author(s) -
Hisamitsu Takashi,
Ben Ammar Youssef,
Nakamura Tomoe Y.,
Wakabayashi Shigeo
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a242-c
Subject(s) - intracellular ph , extracellular , chemistry , mutant , intracellular , cysteine , intermolecular force , transporter , biophysics , sodium–hydrogen antiporter , biochemistry , microbiology and biotechnology , enzyme , molecule , biology , sodium , gene , organic chemistry
The Na + /H + exchanger 1 (NHE1) is the ubiquitous plasma membrane transporter which regulates the intracellular pH (pHi) and cell volume. The NHE1 is known to form homodimer, but the physiological role of dimerization is not well established. Two approaches were taken for addressing this question; to examine whether 1) co‐expression of transport‐deficient mutant NHE1 inhibits the exchange activity, and 2) intermolecular cross‐linking inhibits the activity through restricting the expected cooperative motion between NHE1 subunits. Forced expression of NHE1 mutant E262I which is catalytically inactive, but normal in plasma membrane expression, dramatically reduced the exchange activity of the endogenous NHE1 at near neutral pHi range and abolished growth factor activation, indicating that it exerted the dominant negative effect. On the other hand, by extensive search we found that intermolecular cysteine cross‐linking at Ser 375 in the putative extracellular loop 5, greatly reduced the exchange activity in the physiological pHi range, while treatment with other monofunctional cysteine modifiers had no effect on function of the S375C mutant. These results suggest that cross‐linking inhibited the NHE1 activity by restricting a coupled motion between the two subunits during transport. Thus, we concluded that dimerization of NHE1 is crucial for the exchange activity at least in the physiological pHi range.