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  • The EMBO Journal (1999) 18, 3558 - 3563
  • doi:10.1093/emboj/18.13.3558

Projection structure of NhaA, a secondary transporter from Escherichia coli, at 4.0 Å resolution

Karen A. Williams1, Ulrike Geldmacher-Kaufer1, Etana Padan2, Shimon Schuldiner2 and Werner Kühlbrandt1

  1. Max-Planck-Institute of Biophysics, Department of Structural Biology, Heinrich-Hoffmann-Strasse 7, D-60528 Frankfurt am Main, Germany
  2. The Hebrew University of Jerusalem, Department of Microbial and Molecular Ecology, The Institute of Life Sciences, 91904 Jerusalem, Israel

Correspondence to:

Karen A. Williams, E-mail: williams@biophys.mpg.de

Received 8 March 1999; Accepted 18 May 1999; Revised 18 May 1999

Electron cryomicroscopy of frozen-hydrated two-dimensional crystals of NhaA, a Na+/H+ antiporter from Escherichia coli predicted to have 12 transmembrane alpha-helices, has facilitated the calculation of a projection map of NhaA at 4.0 Å resolution. NhaA was homologously expressed in E.coli with a His6 tag, solubilized in dodecyl maltoside and purified in a single step using Ni2+ affinity chromatography. Two-dimensional crystals were obtained after reconstitution of purified protein with E.coli lipids. The projection map reveals that this secondary transporter has a highly asymmetric structure in projection. NhaA exhibits overall dimensions of approx38times48 Å with a ring-shaped density feature probably corresponding to a bundle of tilted helices, adjacent to an elongated region of density containing several peaks indicative of transmembrane helices. Two crystal forms with p22121 symmetry show tightly packed dimers of NhaA which differ in the interactions between adjacent dimers. This work provides the first direct glimpse into the structure of a secondary transporter.

  • Keywords:

    • electron cryomicroscopy,
    • Escherichia coli,
    • Na+/H+ antiporter,
    • two-dimensional crystallization