Ar/R selectivity filters of PtXIP2;1 and F-FoXIP. Ar/R selectivity filters of two XIPs, one from a dicot plant (PtXIP2;1) and the other from fungi (F-FoXIP). XIP models were first individually superposed on the experimentally determined structures of GlpF and SoPIP2;1 as described in Figure 3. Residues of XIP models are shown in stick representation with nitrogen and oxygen atoms displayed in blue and red respectively. For other details, see the caption of Figure 3. (A) Ar/R selectivity filter of PtXIP2;1 has three hydrophobic residues and is likely to transport a more hydrophobic solute. (B) The presence of Asn and Arg along with two small residues makes the ar/R selectivity filter of F-FoXIP more hydrophilic and result in a wider constriction. Such XIPs are likely to transport bulkier hydrophilic solutes.