pH-induced structural change in a sodium/proton antiporter from Methanococcus jannaschii.
Na+/H+ antiporters are pH-dependent membrane transport proteins that maintain the homeostasis of H+ and Na+ in living cells. MjNhaP1 from Methanococcus jannaschii, a hyperthermophilic archaeon that grows optimally at 85 degrees C, was cloned and expressed in Escherichia coli. Two-dimensional crystals were obtained from purified protein at pH 4. Electron cryomicroscopy yielded an 8 A projection map. Like the related E. coli antiporter NhaA, MjNhaP1 is a dimer, but otherwise the structures of the two antiporters differ significantly. The map of MjNhaP1 shows elongated densities in the centre of the dimer and a cluster of density peaks on either side of the dimer core, indicative of a bundle of 4-6 membrane-spanning helices. The effect of pH on the structure of MjNhaP1 was studied in situ. A major change in density distribution within the helix bundle, and an approximately 2 A shift in the position of the helix bundle relative to the dimer core occurred at pH 6 and above. The two conformations at low and high pH most likely represent the closed and open states of the antiporter.
Vinothkumar
Kutti R
KR
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
Smits
Sander H J
SH
Kühlbrandt
Werner
W
D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017017:Methanococcus / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D019843:Archaeal Proteins; D029968:Escherichia coli Proteins; C102839:NhaA protein, E coli; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; D006859:Hydrogen; D012964:Sodium