"AQP0 serves a dual function in the lens, acting both as a water channel and as an adhesion molecule. During the differentiation of fibre cells, and as they grow older and become buried more deeply in the lens, AQP0 is cleaved at both termini. This processing seems to be the trigger for junction formation." (Gonen et. al 2005)

The opening screen shows a meshribbon model of the overlayed junctional and non-junctional AQP0 protein.

The green is the non-junctional and the red is the junctional.

In some of the following models, temperature coloring emphasizes areas of less conformational constraint in red.

Junctional Wire Frame

Junctional Wire Frame (Temperature Coloring)

Non-junctional Wire Frame

Non-junctional Wire Frame (Temperature Coloring)

Junctional Cartoon

Non-junctional Cartoon

AQP0 aquaporin pores are mainly lined with alpha helices, which can be seen clearly using the cartoon representation.

Junctional Cartoon and Wireframe

Non-Junctional Cartoon and Wireframe

Junctional spacefill: sphere 0A

Non-junctional spacefill: sphere 0A

Junctional solvent accessible surface: dots

Non-junctional solvent accessible surface: dots

The next surface displays are solid and require calculations with some time delays

Junctional AQP0 model of solvent accessible surface: solid (1.2 A) - surface at center of 1.2 sphere (sasurface)

Non-juntional AQP0 model of solvent accessible surface: solid (1.2 A) - surface at center of 1.2 sphere (sasurface)

Junctional AQPO solvent excluded molecular surface - (solid 1.4 A) - surface at contact with sphere (molecular)

Non-junctional AQPO solvent excluded molecular surface - (solid 1.4 A) - surface at contact with sphere (molecular)

The following contain isosurface modeling of AQP0 in both junctional and non-junctional conformations. The green areas around the center contain residues that are mostly non-polar as they must interact with the lipid membrane.

Both juntional and non-junctional display very similar electrostatic potential distributions. 

Map of Electrostatic potential from non-juctional AQPO with wireframe rendering

It turns out formation of the AQP0 tetrameter is mediated partially through the Trp 34 and Pro 38 residues. Comparison of the structure of junctional AQP0 with that of non-junctional AQP0 indicates that cleavage of the two cytoplasmic termini might lead to a conformational change, "eliminating steric hindrance from Trp 34 and allowing Pro 38 to stabilize the junctional interaction [with other AQP0 monomers]." (Gonen et. al 2005)

"Formation of the junction also seems to correlate with changes in the side-chain positions of residues lining the pore, most importantly in Met 176, resulting in substantial constriction. Three water molecules are trapped in the centre of the water pathway, too far apart from each other to be linked by hydrogen bonds." (Gonen et. al 2005)

Junctional (closed) AQP0 Cartoon with conformation altering residues: Trp 34 (Red), Pro 38 (Purple), Met 176 (Green)