Fig. 4

Modeling of the Asp50Asn mutant (D50N). In order simplify the figure the one letter nomenclature was used for amino acids. The figure was obtained using the software VMD. a and b show the location of D50 (red) in the structure of the channel. c shows the theoretical structural model of the D50N mutant. The direct contact interactions on a radial distribution of 5 Å for each mutant are shown in the corresponding panels. D50 makes contacts with D46, A49 and S183 of the same chain, and Q48, K61 and N62 of a contiguous chain. This residue is located in an internal region of the channel enriched in acidic residues (D46 and E47) balanced with basic residues (R184, K61, and K188). The mutation D50N decreases the negative charge of this environment as well as alters the core of the inter-protomer interactions. The theoretical model shows that the D50N mutation breaks a salt bridge that exists between D50 and K61 and produces a hydrogen bond between the side chain of N50 and D46