Structures were obtained by molecular substitution from published models and were refined using REFMAC (Winn et al. , 2003 ▶ ) and ARP / wARP (Perrakis et al. , 2001 ▶ ) (starting mode... s: lysozyme, PDB entry 1lyz ; thermolysin, 4tln ; stachydrine demethylase, 3vca ; photosystem II, 1fe1 ; Diamond, 1974 ▶ ; Holmes & Matthews, 1981 ▶ ; Daughtry et al. , 2012 ▶ ; Zouni et al. , 2001 ▶ ).