Fig. 11

Alternative cysteine rotamers at the selectivity filter of salmon AQP8. Cysteine 53 is modelled in two alternative conformations. The rotamer colored in green is turned towards arginine 213 at HE^P with a distance of 3.3 Å. If not oriented towards arginine 213, cysteine 53 can hydrogen bond to a serine (S128) in helix 3. Hydrogen bonds are depicted as dashes, and the pore is contoured by a dotted surface. The histidine at H2^P (H72) stabilizes the position of arginine 213 by hydrogen bonding to the secondary ketimine