<p>(A) Topology plot showing membrane-spanning helices (H1–H6) and intervening loops (A–E). Homologous regions in the internal repeat are indicated by colors. The five positions of an extended selectivity filter are marked according to the key within the figure. The glycine (Gly 1) corresponding to the initiator methionine in <i>At</i>TIP2;1 is shaded in dark cyan next to a dashed line representing the TEV cleavage site, and the N-terminal deca-His tag is shaded in purple. (B) Two short helices (HB and HE) in loop B and E, connected via conserved NPA-motifs, form a seventh transmembrane segment. All membrane-spanning segments are tilted in the membrane, but it is most accentuated in helices H3, H6, HB, and HE facing the lipid bilayer. (C) Eight water molecules form a single file in the main pore of the monomer, connecting the cytosolic and vacuolar vestibules. At the top right, five additional water molecules are seen in a side pore underneath loop C. (D) <i>At</i>TIP2;1 tetramer viewed from the vacuolar side. Monomers are shown in surface representation and in the cartoon representation used in (B) and (C).</p
