Structure of the water channel AgpZ from Escherichia coli revealed by electron crystallography

P. Ringler, M. J. Borgnia, H. Stahlberg, P. C. Maloney, P. Agre, A. Engel

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Molecular water channels (aquaporins) allow living cells to adapt to osmotic variations by rapid and specific diffusion of water molecules. Aquaporins are present in animals, plants, algae, fungi and bacteria. Here we present an electron microscopic analysis of the most ancient water channel described so far: the aquaporin Z (AqpZ) of Escherichia coli. A recombinant AqpZ with a poly(histidine) tag at the N terminus has been constructed, overexpressed and purified to homogeneity. Solubilized with octylglucoside, the purified AqpZ remains associated as a homotetramer, and assembles into highly ordered two-dimensional tetragonal crystals with unit cell dimensions a = b = 95 Å, γ = 90°when reconstituted by dialysis in the presence of lipids. Three-dimensional reconstruction of negatively stained lattices revealed the p4212 packing arrangement that is also observed with the human erythrocyte water channel (AQP1). The 8 Å projection map of the AqpZ tetramer in frozen hydrated samples is similar to that of AQP1, consistent with the high sequence homology between these proteins.

Original languageEnglish (US)
Pages (from-to)1181-1190
Number of pages10
JournalJournal of molecular biology
Issue number5
StatePublished - Sep 3 1999


  • 2D crystallization
  • Aquaporin
  • Electron crystallography
  • Major integral protein family
  • STEM

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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