Overlay of the D, E and de ɑ-helices that form the QB pocket, and terbutryn occupying the pocket in the Rba. sphaeroides reaction centre (yellow (online) or light-grey (print)) and the T. elongatus PSII (cyan (online) or dark-grey (print)). Prepared using Protein Data Bank entries 2BNP (Katona et al., 2005) and 3PRQ (Broser et al., 2010), and PyMOL (Schrödinger, LLC). For a stereo, colour representation see Supplementary Fig. 1.