(a) SeDDM molecules in an LTC4S trimer with anomalous difference Fourier map. The red mesh is the anomalous difference Fourier map calculated from the refined phases and the anomalous differences of the peak data set contoured at 5σ of an asymmetric unit. SeDDM is represented by a stick model with yellow C atoms. The blue cartoon model indicates a monomer in the LTC4S trimer and the roman numerals show the sequential order of the helices. Magnified views of the SeDDM binding sites are shown in (b), (c) and (d), with the electron densities of the SeDDM molecules represented by a blue mesh contoured at 1.0σ. (b) SeDDM and its surrounding residues in site 1. The dashed lines indicate hydrogen bonds between SeDDM and amino-acid residues. The wheat-coloured models labelled IV* and V* indicate helices IV and V of a twofold-symmetry-related molecule in the crystal packing. (c) SeDDM of site 2. The neighbouring alkyl chain and its election density are also displayed. (d) SeDDM in site 3. The bound glutathione is represented by green C atoms.