Figure 1.

Aquaporin structure: (a) primary sequence of Aquaporin 4 (AQP4), the water channel with the highest recorded water permeability (see Table 1), highlighting the NPA (Asn-Pro-Ala) residues in yellow; (b) tertiary structure of the AQP4 homotetramer showing four water pores (marked with a blue dot) and the ‘fifth pore’ produced by formation of the tetramer (marked with a red dot). Adapted from an image originally published in [33].