Fig. 5. Ternary anion–π–cation and anion–π–π interactions in biological systems. (a) Pseudouridine synthase TruB complexed to RNA (PDB code 1K8W), where SO₄–π–Arg interactions are shown. (b) Active site of CEAS complexed to dipotassium l-(+)-tartrate (PDB code ; 2IHU), where Glu–π–K⁺ interactions are shown. (c) Active site of PfGST (PDB code ; 1OKT), where a Glu–π–π interaction is shown.