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Crystal structure of the outer membrane active transporter FepA from Escherichia coli

Nature Structural Biology volume 6, pages 56–63 (1999)Cite this article

Abstract

Integral outer membrane receptors for iron chelates and vitamin B 12 carry out specific ligand transport against a concentration gradient. Energy for active transport is obtained from the proton–motive force of the inner membrane through physical interaction with TonB–ExbB–ExbD, an inner membrane complex. Here we report the crystal structure of an active transport, outer membrane receptor at 2.4 Å resolution. Two distinct functional domains are revealed: (i) a 22–stranded β–barrel that spans the outer membrane and contains large extracellular loops which appear to function in ligand binding; and (ii) a globular N–terminal domain that folds into the barrel pore, inhibiting access to the periplasm and contributing two additional loops for potential ligand binding. These loops could provide a signaling pathway between the processes of ligand recognition and TonB–mediated transport. The blockage of the pore suggests that the N–terminal domain must undergo a conformational rearrangement to allow ligand transport into the periplasm.

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Figure 1: Ribbon diagram of FepA.
Figure 2: Topology of the FepA barrel, using amino acid sequence in one–letter code.
Figure 3: 2Fo – Fc stereo electron density map at 2.4 Å resolution, contoured at 1.4σ.
Figure 4: The fold of the polypeptide chain.
Figure 5: Blockage of the pore by the N–terminal domain as viewed from the periplasm.
Figure 6: Anomalous scattering difference Fourier map contoured at 4.0σ (violet) superimposed on a stereo ribbon diagram of FepA.
Figure 7: Interactions in the TonB box.

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Acknowledgements

We thank Z. Wang for help with in–house data collection; and M. Capel and C. Ogata for help with synchrotron data collection. D.v.d.H. acknowledges support from the NIH. S.K.B. acknowledges support from the American Cancer Society. J.D. is an Investigator in the Howard Hughes Medical Institute.

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  1. Susan K. Buchanan

    Present address: Department of Crystallography, Birkbeck College, University of London, Malet Street, London, WC1E 7HX, UK

Authors and Affiliations

  1. Howard Hughes Medical Institute, and Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, 75235–9050, Texas, USA

    Susan K. Buchanan, Barbara S. Smith, Di Xia, Lothar Esser, Maya Palnitkar & Johann Deisenhofer

  2. Department of Chemistry and Biochemistry, The University of Oklahoma, 620 Parrington Oval, Norman, 73019–0370, Oklahoma, USA

    Lalitha Venkatramani, Ranjan Chakraborty & Dick van der Helm

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Buchanan, S., Smith, B., Venkatramani, L. et al. Crystal structure of the outer membrane active transporter FepA from Escherichia coli. Nat Struct Mol Biol 6, 56–63 (1999). https://doi.org/10.1038/4931

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