Fig. 4

Side-chain conformations of the salt bridges introduced in the variant A55R/N156E-H239E, resolution 1.67 Å. a Residue Arg55 has two alternate locations, state A and B, with 0.5 occupancy for each state; and residue Glu156 includes two states, C and D, sharing equal occupancies (0.5). b Rigid hydrogen bonding and salt bridges between residues surrounding amino acid Glu239