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

Authors
  • Scheuring, S
  • Ringler, P
  • Borgnia, M
  • Stahlberg, H
  • Müller, D J
  • Agre, P
  • Engel, A
Type
Published Article
Journal
The EMBO Journal
Publisher
EMBO
Publication Date
Sep 15, 1999
Volume
18
Issue
18
Pages
4981–4987
Identifiers
PMID: 10487750
Source
Medline
License
Unknown

Abstract

Aquaporins form a large family of membrane channels involved in osmoregulation. Electron crystallography has shown monomers to consist of six membrane spanning alpha-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 p42(1)2 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.

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