Table 1.

AQP crystal structures. Unrevealing the gating mechanism requires atomic resolution models of the end state in order to define the sequence of transitions that connect the open and closed states.

AQP	Species	Res. (Å)	PDB	Comments	References
AQP0	Bos taurus	1.9 2.4 2.5 2.24 7.01 25	2B6O 2B6P 3M9I 1YMG 2C32 3J41	✓Association mode between AQP0 tetramers from juxtaposed membranes in the eye lens ✓CaM regulates multimeric channels by facilitating cooperativity between adjacent subunits	[50,54,55,56]
AQP1	Homo sapiens Bos taurus	3.8 3.7 2.2 3.28 3.54	1FQY 1IH5 1J4N 4CSK 1H6I 6POJ	✓Structural determinants for water permeation are extensively described	[14,52,57,58,59]
AQP2	Homo sapiens	2.75 3.7 3.05	4NEF 4OJ2 6QF5	✓Trafficking capacity from intracellular vesicles to the plasma membrane	[60,61]
AQP4	Rattus Homo sapiens	3.2 2.8 1.8 10	2D57 2ZZ9 3GD8 3IYZ	✓Array formation and cell adhesion ✓Water conductance mechanism ✓Role of the N terminus of AQP4 in the stabilization of orthogonal arrays	[62,63,64,65]
AQP5	Homo sapiens	2.2 2.6 3.5	3D9S 5C5X 5DYE	✓Multiple phosphorylation sites	[66,67]
AQP7	Homo sapiens	2.2 1.9 3.99 3.70	6QZJ 6QZI 6N1G 6KXW	✓Structure of AQP7 bound to glycerol	[68,69,70]
AQP10	Homo sapiens	2.3	6F7H		[71]
AQPM	Methanothermobacter marburgensis Archaeoglobus fulgidus	1.68 2.3 3.0	2F2B 2EVU 3NE2	✓A subdivision between water-selective aquaporins, and water-plus-glycerol-conducting aquaglyceroporins	[72]
GlpF	Escherichia coli	2.2 2.8 2.1 2.7	1FX8 1LDA 1LDF 1LDI	✓Primary permeant substrate glycerol	[73,74]
AQPZ	Escherichia coli	2.5 3.2 2.2 2.3 2.55 2.4	1RC2 2ABM 2O9D 2O9E 2O9F 3NK5	✓Two distinct Arg-189 conformations associated with water permeation	[75,76,77,78]
PfAQP	Plasmodium falciparum	2.05	3C02	✓The two NPA regions bear substitutions to Asn-Leu-Ala (NLA) and Asn-Pro-Ser (NPS), might participate in preserving the orientation of the selectivity filter asparagines in the center of the channel	[79]
AQY1	Pichia pastoris	1.15 1.4 0.88 1.3	2W2E 2W1P 3ZOJ 5BN2	✓Proposed gating mechanism regulated by a combination of phosphorylation and mechanosensitivity. ✓Ultra-high resolution allowed hydrogens to be modelled inside the water-conducting channel.	[80,81]
PIP2;1	Spinacia oleracea	2.1 (close) 3.9 (open) 2.3 2.95 2.05	1Z98 2B5F 3CLL 3CN6 3CN5	✓Molecular dynamics simulations of the initial events governing gating ✓S115E and S274E single SoPIP2;1 mutants and the corresponding double mutant ✓Crystal structure of the AQP at low pH, reveals for the first time the structural basis for how this pH-sensitive histidine helps to keep the aquaporin in a closed state	[35,38,82]
PIP2;4	Arabidopsis thaliana	3.7	6QIM		[83]
TIP2;1	Arabidopsis thaliana	1.18	5I32	✓Ammonia-permeable aquaporin ✓Extended selectivity filter with the conserved arginine of the filter adopting a unique unpredicted position	[84]