Fig. 6
From: Single amino acid substitutions in the selectivity filter render NbXIP1;1α aquaporin water permeable
Cartoon representation of the homology model of NbXIP1;1αwt and the structure of PfAQP. The high resolution X-ray structure (PDB 5I32) of AtTIP2;1 was used as template to model NbXIP1;1αwt [14]. a Side view (upper panel) and top view (below) of NbXIP1;1αwt model, showing the general aquaporin monomeric fold with 6 transmembrane helices and 2 half helices with interconnecting loops. The deletions in loop C (orange at the top) and loop D (short: pink, long: pink + orange) are also indicated. b Close-up of the salt-bridge between arginine (R263) of the ar/R selectivity filter and aspartate (D80) in helix 1 in the model. Except in the NbXIP1;1αL79G/V242I model, the arginine (R263) also forms hydrogen bonds to the carbonyls of the backbone in loop E. This seems to be valid for all but one model of NbXIP1;1α in this study c. In the PfAQP (PDB ID 3CO2), the arginine (R196) at position HEP in the ar/R filter interacts with an acidic residue (E28) in a corresponding position, but in contrast to the XIP-models the arginine of PfAQP also forms hydrogen bonds to a carbonyl (W124) of the loop C backbone [45]