Aquaglyceroporins, one channel for two molecules.

In the light of the recently published structure of GlpF and AQP1, we have analysed the nature of the residues which could be involved in the formation of the selectivity filter of aquaporins, glycerol facilitators and aquaglyceroporins. We demonstrate that the functional specificity for major intrinsic protein (MIP) channels can be explained on one side by analysing the polar environment of the residues that form the selective filter. On the other side, we show that the channel selectivity could be associated with the oligomeric state of the membrane protein. We conclude that a non-polar environment in the vicinity of the top of helix 5 could allow aquaglyceroporins and GlpF to exist as monomers within the hydrophobic environment of the membrane.