Figure 1.

Schematic demarcation of the polypeptide sequence of AQP1 into the six transmembrane α-helices TM1 to TM6, the cytoplasmic (H1) and extracellular (H3) α-helices in the two NPA loops, the short α-helix (H2) at the extracellular edge of TM3, and the intervening connecting loops. Amino acids belonging to the transmembrane helices (whose side chains either line the channel or point into the channel) are colored green. The mercurial-sensitive C189 (colored red) and the analogous A73 are indicated. Residues in the TM3-TM4 linker that line the entrance of the aqueous pathway on the extracellular side are colored light green. The color scheme indicated for TM1–TM6, H2, and the color white for H1, H3, and the connecting segments, follow in Fig. 2 a and b, Fig. 3, and Fig. 5b.