Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

The structure of the KtrAB potassium transporter

Nature volume 496, pages 323–328 (2013)Cite this article

Subjects

Abstract

In bacteria, archaea, fungi and plants the Trk, Ktr and HKT ion transporters are key components of osmotic regulation, pH homeostasis and resistance to drought and high salinity. These ion transporters are functionally diverse: they can function as Na+ or K+ channels and possibly as cation/K+ symporters. They are closely related to potassium channels both at the level of the membrane protein and at the level of the cytosolic regulatory domains. Here we describe the crystal structure of a Ktr K+ transporter, the KtrAB complex from Bacillus subtilis. The structure shows the dimeric membrane protein KtrB assembled with a cytosolic octameric KtrA ring bound to ATP, an activating ligand. A comparison between the structure of KtrAB–ATP and the structures of the isolated full-length KtrA protein with ATP or ADP reveals a ligand-dependent conformational change in the octameric ring, raising new ideas about the mechanism of activation in these transporters.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Structure of the KtrAB K+ transporter.
Figure 2: KtrB subunit.
Figure 3: Ligand regulation of KtrAB transporter.
Figure 4: Conformational changes in the KtrA octameric ring.
Figure 5: Models for KtrAB activation.

Similar content being viewed by others

Accession codes

Primary accessions

Protein Data Bank

Data deposits

Structures have been deposited in the Protein Data Bank under accessions 4J7C (KtrAB complex), 4J90 (KtrA–ATP) and 4J91 (KtrA–ADP).

References

  1. Corratgé-Faillie, C. et al. Potassium and sodium transport in non-animal cells: the Trk/Ktr/HKT transporter family. Cell. Mol. Life Sci. 67, 2511–2532 (2010)

    Article  Google Scholar 

  2. Durell, S. R., Hao, Y., Nakamura, T., Bakker, E. P. & Guy, H. R. Evolutionary relationship between K+ channels and symporters. Biophys. J. 77, 775–788 (1999)

    Article  CAS  Google Scholar 

  3. Nakamura, T., Yuda, R., Unemoto, T. & Bakker, E. P. KtrAB, a new type of bacterial K+-uptake system from Vibrio alginolyticus. J. Bacteriol. 180, 3491–3494 (1998)

    CAS  PubMed  PubMed Central  Google Scholar 

  4. Hänelt, I. et al. KtrB, a member of the superfamily of K+ transporters. Eur. J. Cell Biol. 90, 696–704 (2011)

    Article  Google Scholar 

  5. Tholema, N., Bakker, E. P., Suzuki, A. & Nakamura, T. Change to alanine of one out of four selectivity filter glycines in KtrB causes a two orders of magnitude decrease in the affinities for both K+ and Na+ of the Na+ dependent K+ uptake system KtrAB from Vibrio alginolyticus. FEBS Lett. 450, 217–220 (1999)

    Article  CAS  Google Scholar 

  6. Albright, R. A., Joh, K. & Morais-Cabral, J. H. Probing the structure of the dimeric KtrB membrane protein. J. Biol. Chem. 282, 35046–35055 (2007)

    Article  CAS  Google Scholar 

  7. Maser, P. et al. Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants. Proc. Natl Acad. Sci. USA 99, 6428–6433 (2002)

    Article  ADS  CAS  Google Scholar 

  8. Tholema, N. et al. All four putative selectivity filter glycine residues in KtrB are essential for high affinity and selective K+ uptake by the KtrAB system from Vibrio alginolyticus. J. Biol. Chem. 280, 41146–41154 (2005)

    Article  CAS  Google Scholar 

  9. Cao, Y. et al. Crystal structure of a potassium ion transporter, TrkH. Nature 471, 336–340 (2011)

    Article  ADS  CAS  Google Scholar 

  10. Doyle, D. A. et al. The structure of the potassium channel: molecular basis of K+ conduction and selectivity. Science 280, 69–77 (1998)

    Article  ADS  CAS  Google Scholar 

  11. Jiang, Y. et al. The open pore conformation of potassium channels. Nature 417, 523–526 (2002)

    Article  ADS  CAS  Google Scholar 

  12. Jiang, Y. et al. Crystal structure and mechanism of a calcium-gated potassium channel. Nature 417, 515–522 (2002)

    Article  ADS  CAS  Google Scholar 

  13. Wu, Y., Yang, Y., Ye, S. & Jiang, Y. Structure of the gating ring from the human large-conductance Ca2+-gated K+ channel. Nature 466, 393–397 (2010)

    Article  ADS  CAS  Google Scholar 

  14. Yuan, P., Leonetti, M. D., Pico, A. R., Hsiung, Y. & MacKinnon, R. Structure of the human BK channel Ca2+-activation apparatus at 3.0 Å resolution. Science 329, 182–186 (2010)

    Article  ADS  CAS  Google Scholar 

  15. Yuan, P., Leonetti, M. D., Hsiung, Y. & MacKinnon, R. Open structure of the Ca2+ gating ring in the high-conductance Ca2+-activated K+ channel. Nature 481, 94–97 (2012)

    Article  ADS  CAS  Google Scholar 

  16. Holtmann, G., Bakker, E. P., Uozumi, N. & Bremer, E. KtrAB and KtrCD: two K+ uptake systems in Bacillus subtilis and their role in adaptation to hypertonicity. J. Bacteriol. 185, 1289–1298 (2003)

    Article  CAS  Google Scholar 

  17. Berry, S. et al. Potassium uptake in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 mainly depends on a Ktr-like system encoded by slr1509 (ntpJ). FEBS Lett. 548, 53–58 (2003)

    Article  CAS  Google Scholar 

  18. Matsuda, N. et al. Na+-dependent K+ uptake Ktr system from the cyanobacterium Synechocystis sp. PCC 6803 and its role in the early phases of cell adaptation to hyperosmotic shock. J. Biol. Chem. 279, 54952–54962 (2004)

    Article  CAS  Google Scholar 

  19. Hanelt, I. et al. Gain of function mutations in membrane region M2C2 of KtrB open a gate controlling K+ transport by the KtrAB system from Vibrio alginolyticus. J. Biol. Chem. 285, 10318–10327 (2010)

    Article  Google Scholar 

  20. Kroning, N. et al. ATP binding to the KTN/RCK subunit KtrA from the K+-uptake system KtrAB of Vibrio alginolyticus: its role in the formation of the KtrAB complex and its requirement in vivo. J. Biol. Chem. 282, 14018–14027 (2007)

    Article  Google Scholar 

  21. Albright, R. A., Ibar, J. L., Kim, C. U., Gruner, S. M. & Morais-Cabral, J. H. The RCK domain of the KtrAB K+ transporter: multiple conformations of an octameric ring. Cell 126, 1147–1159 (2006)

    Article  CAS  Google Scholar 

  22. Roosild, T. P., Miller, S., Booth, I. R. & Choe, S. A mechanism of regulating transmembrane potassium flux through a ligand-mediated conformational switch. Cell 109, 781–791 (2002)

    Article  CAS  Google Scholar 

  23. Heginbotham, L., Kolmakova-Partensky, L. & Miller, C. Functional reconstitution of a prokaryotic K+ channel. J. Gen. Physiol. 111, 741–749 (1998)

    Article  CAS  Google Scholar 

  24. Ye, S., Li, Y., Chen, L. & Jiang, Y. Crystal structures of a ligand-free MthK gating ring: insights into the ligand gating mechanism of K+ channels. Cell 126, 1161–1173 (2006)

    Article  CAS  Google Scholar 

  25. Olesen, C. et al. The structural basis of calcium transport by the calcium pump. Nature 450, 1036–1042 (2007)

    Article  ADS  CAS  Google Scholar 

  26. Cuello, L. G. et al. Structural basis for the coupling between activation and inactivation gates in K+ channels. Nature 466, 272–275 (2010)

    Article  ADS  CAS  Google Scholar 

  27. Trudeau, M. C. Unlocking the mechanisms of HCN channel gating with locked-open and locked-closed channels. J. Gen. Physiol. 140, 457–461 (2012)

    Article  CAS  Google Scholar 

  28. Hilf, R. J. & Dutzler, R. A prokaryotic perspective on pentameric ligand-gated ion channel structure. Curr. Opin. Struct. Biol. 19, 418–424 (2009)

    Article  CAS  Google Scholar 

  29. Nimigean, C. M. A radioactive uptake assay to measure ion transport across ion channel-containing liposomes. Nature Protocols 1, 1207–1212 (2006)

    Article  CAS  Google Scholar 

  30. Kabsch, W. Xds. Acta Crystallogr. D 66, 125–132 (2010)

    Article  CAS  Google Scholar 

  31. Leslie, A. G. The integration of macromolecular diffraction data. Acta Crystallogr. D 62, 48–57 (2006)

    Article  Google Scholar 

  32. Kelley, L. A. & Sternberg, M. J. Protein structure prediction on the Web: a case study using the Phyre server. Nature Protocols 4, 363–371 (2009)

    Article  CAS  Google Scholar 

  33. McCoy, A. J. et al. Phaser crystallographic software. J. Appl. Crystallogr. 40, 658–674 (2007)

    Article  CAS  Google Scholar 

  34. Adams, P. D. et al. PHENIX: a comprehensive Python-based system for macromolecular structure solution. Acta Crystallogr. D 66, 213–221 (2010)

    Article  CAS  Google Scholar 

  35. Kleywegt, G. J. & Jones, T. A. Software for handling macromolecular envelopes. Acta Crystallogr. D 55, 941–944 (1999)

    Article  CAS  Google Scholar 

  36. Emsley, P. & Cowtan, K. Coot: model-building tools for molecular graphics. Acta Crystallogr. D 60, 2126–2132 (2004)

    Article  Google Scholar 

  37. Strong, M. et al. Toward the structural genomics of complexes: crystal structure of a PE/PPE protein complex from Mycobacterium tuberculosis. Proc. Natl Acad. Sci. USA 103, 8060–8065 (2006)

    Article  ADS  CAS  Google Scholar 

  38. Schrodinger, LLC. The PyMOL Molecular Graphics System, Version 1.3r1 (2010)

    Google Scholar 

  39. Gille, C. & Frommel, C. STRAP: editor for STRuctural Alignments of Proteins. Bioinformatics 17, 377–378 (2001)

    Article  CAS  Google Scholar 

  40. Gouet, P., Robert, X. & Courcelle, E. ESPript/ENDscript: Extracting and rendering sequence and 3D information from atomic structures of proteins. Nucleic Acids Res. 31, 3320–3323 (2003)

    Article  CAS  Google Scholar 

  41. Ho, B. K. & Gruswitz, F. HOLLOW: generating accurate representations of channel and interior surfaces in molecular structures. BMC Struct. Biol. 8, 49 (2008)

    Article  Google Scholar 

  42. Winn, M. D. et al. Overview of the CCP4 suite and current developments. Acta Crystallogr. D 67, 235–242 (2011)

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We are grateful for access to ID14-1/ID14-4/ID-29 at ESRF (through the Portuguese BAG), PXII at SLS, XRD1 at ELETTRA and PROXIMA1 at SOLEIL and thank the respective support staff. A.S. was supported by FEBS (Long term fellowship). This work was funded by EMBO (Installation grant), by FEDER funds through the Operational Competitiveness Program–COMPETE and by National Funds through FCT–Fundação para a Ciência e a Tecnologia under the projects FCOMP-01-0124-FEDER-022718 (PEst-C/SAU/LA0002/2011), FCOMP-01-0124-FEDER-009028 (PTDC/BIA-PRO/099861/2008) and FCOMP-01-0124-FEDER-010781 (PTDC/QUI-BIQ/105342/2008). We also thank G. Gabant and M. Cadene at the ‘Plateforme de Spectrometrie de Masse’ at CBM, CNRS, Orleans for mass spectrometry analysis, and C. Harley for critical reading of the manuscript.

Author information

Authors and Affiliations

  1. IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, Porto 4150-180, Portugal,

    Ricardo S. Vieira-Pires, Andras Szollosi & João H. Morais-Cabral

Authors
  1. Ricardo S. Vieira-Pires
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Andras Szollosi
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. João H. Morais-Cabral
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

R.S.V.-P. performed all crystallographic work with the support of J.H.M.-C.; R.S.V.-P. and A.S. performed the functional and biochemical characterization; J.H.M.-C., R.S.V.-P. and A.S. designed experiments and wrote the manuscript.

Corresponding author

Correspondence to João H. Morais-Cabral.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-10, which illustrates different aspects of the structural and biochemical characterization of the KtrAB potassium transporter, Supplementary Table 1 showing statistics for diffraction data and crystallographic refinement for the KtrAB, KtrA-ATP and KtrA-ADP structures, and a Supplementary Discussion containing detailed information about the contact regions established between the KtrB homodimer and KtrA ring, as well as discussion of the activation models presented in the main text. (PDF 27413 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Vieira-Pires, R., Szollosi, A. & Morais-Cabral, J. The structure of the KtrAB potassium transporter. Nature 496, 323–328 (2013). https://doi.org/10.1038/nature12055

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature12055

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing