Contacts between Glt_Ph asymmetric IFS protomers related by noncrystallographic symmetry (PDB code 4X2S ). Superposition of unlocked protomers B (green) and C (gray) and a locked protomer A (yellow). Chain C_sym of a symmetry molecule that forms an interface with chain B is shown in blue. Chains B and C_sym are symmetry mates, where steric clashes between the loop 4c-5 (chain B) and helix HP1b (chain C_sym) may have caused the shift of 4c-5 hairpin (shown with a dashed arrow), creating an “unlocked” conformation. Cartoon representation; amino acid residues that could cause steric clashes are shown as sticks.