FIG. 4.

Structural rationale of the designated mutations in A. niger PhyA. Green dotted lines represent the hydrogen bond interactions. (A) A comparison of hydrogen bonding between the WT (left) and the double mutant A58E P65S (right) shows that two new hydrogen bonds with distances of 3.01 and 3.66 Å, respectively, were introduced between substitutions E58 and S65 (right). (B) The single mutation Q191R removes a repulsive ionic interaction in the loop region, and R191 can interact with D184 through a salt bridge to stabilize the structure. (C) The single mutation T271R can render the residue interacting with D267 through a salt bridge and also introduces a new hydrogen bond between R271 and S270 with a distance of 2.71 Å.