High resolution AFM topographs of the Escherichia coli water channel aquaporin Z

Simon Scheuring, Philippe Ringler, Mario Borgnia, Henning Stahlberg, Daniel J. Müller, Peter Agre, Andreas Engel

Research output: Contribution to journalArticlepeer-review

155 Scopus citations


Aquaporins form a large family of membrane channels involved in osmoregulation. Electron crystallography has shown monomers to consist of six membrane spanning α-helices confirming sequence based predictions. Surface exposed loops are the least conserved regions, allowing differentiation of aquaporins. Atomic force microscopy was used to image the surface of aquaporin Z, the water channel of Escherichia coli. Recombinant protein with an N-terminal fragment including 10 histidines was isolated as a tetramer by Ni-affinity chromatography, and reconstituted into two-dimensional crystals with p4212 symmetry. Small crystalline areas with p4 symmetry were found as well. Imaging both crystal types before and after cleavage of the N-termini allowed the cytoplasmic surface to be identified; a drastic change of the cytoplasmic surface accompanied proteolytic cleavage, while the extracellular surface morphology did not change. Flexibility mapping and volume calculations identified the longest loop at the extracellular surface. This loop exhibited a reversible force-induced conformational change.

Original languageEnglish (US)
Pages (from-to)4981-4987
Number of pages7
JournalEMBO Journal
Issue number18
StatePublished - Sep 15 1999


  • Atomic force microscopy
  • Bacterial water channel
  • Loops
  • Sidedness
  • Volume

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)


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