Correlating structure, dynamics, and function in transmembrane segment VII of the Na+/H+ exchanger isoform 1
Tyler Reddy1, Xiuju Li, Larry Fliegel
1Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada B3H 1X5.
Biochimica Et Biophysica Acta
|July 15, 2009
Summary
The seventh transmembrane segment of the human sodium-hydrogen exchanger isoform 1 (Na+/H+ exchanger 1) undergoes conformational changes. These dynamics are crucial for proton translocation and exchanger function.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- The seventh transmembrane segment (TM7) of the human Na+/H+ exchanger isoform 1 (NHE1) is critical for its function.
- Previous studies indicated structural interruptions and conformational dynamics within TM7.
Purpose of the Study:
- To correlate the structure, dynamics, and function of the NHE1 TM7 segment.
- To investigate the role of conformational exchange in proton translocation.
Main Methods:
- Utilized (15)N nuclear magnetic resonance (NMR) relaxation analysis.
- Performed functional mutagenesis studies on the full-length exchanger.
- Integrated previous structural and mutagenesis data.
Main Results:
- Residues G261, L264, and A268 in TM7 exhibit dynamics best explained by a mathematical model incorporating chemical exchange.
- A segment from G261 to A268 samples different conformations on the microsecond-millisecond timescale, suggesting an alternating-access mechanism.
- Bulky isoleucine substitutions at key residues (F260I, G261I, E262I, S263I, A268I) abrogated exchanger activity.
Conclusions:
- Chemical exchange on an intermediate timescale is consistent with E262 bending away from the cytosol during proton translocation.
- The dynamics of the G261-A268 segment are functionally important for NHE1 activity.
- Mutagenesis data corroborate the functional significance of chemical exchange in this region.
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