Covalently Linking Oligomerization-Impaired GlpF Protomers Does Not Completely Re-establish Wild-Type Channel Activity.

Integral membrane proteins of the aquaporin family facilitate rapid water flux across cellular membranes in all domains of life. Although the water-conducting pore is clearly defined in an aquaporin monomer, all aquaporins assemble into stable tetramers. In order to investigate the role of protomer⁻protomer interactions, we analyzed the activity of heterotetramers containing increasing fractions of mutated monomers, which have an impaired oligomerization propensity and activity.

The GlpF residue Trp219 is part of an amino-acid cluster crucial for aquaglyceroporin oligomerization and function.

The vestibule loop regions of aquaglyceroporins are involved in accumulation of glycerol inside the channel pore. Even though most loop regions do not show high sequence similarity among aquaglyceroporins, loop E is highly conserved in aquaglyceroporins, but not in members of the homologous aquaporins. Specifically, a tryptophan residue is extremely conserved within this loop.