AqpZ
AqpZ, or Aquaporin Z, is a water channel protein found in bacteria, most notably Escherichia coli. It belongs to the aquaporin superfamily and functions to facilitate rapid, selective water movement across the cell membrane in response to osmotic gradients. AqpZ proteins are typically present as tetramers in the inner membrane, with each monomer forming its own water pore. Each subunit contains six transmembrane helices and two highly conserved NPA (asparagine-proline-alanine) motifs that contribute to pore formation and proton exclusion. The narrowest part of the pore is the ar/R constriction, formed by residues from the surrounding helices, which helps define water selectivity and prevents proton leakage.
Functionally, AqpZ mediates fast water transport to help regulate cell volume during hypo- and hypertonic stress.
Structural studies, including X-ray crystallography, have revealed the tetrameric arrangement and the hourglass-shaped pore architecture of
AqpZ homologues are distributed across many Gram-negative bacteria and some archaea, indicating a conserved role in