Fig. 2. Molecular characterization of the SepF–FtsZ interaction.

a Schematic outline of SepF domains and sequence alignment of selected SepF homologs (Cgl, C. glutamicum; Mtb, M. tuberculosis; Bsu, B. subtilis). Secondary structure elements are shown above the sequences. b Schematic outline of FtsZ domains and FtsZ_CTD sequence alignment of selected homologs (Eco, E. coli). Asterisks (*) indicate strictly conserved positions in the alignment and residues involved in SepF binding are shown in bold. c Crystal structure of the SepF dimer in complex with two FtsZ_CTD peptides. The orientations of the N- and C- termini of SepF and FtsZ are compatible with membrane binding on one hand and Z-ring formation on the other. d Detailed view of the FtsZ-binding pocket in SepF showing residues involved in protein–protein interactions (see Supplementary Fig. 8 for details). Conserved FtsZ_CTD residues D₄₃₆, P₄₃₈, and F₄₄₀ are labeled (*), and SepF residues K125 and F131 were those mutated to abolish FtsZ binding. e FtsZ polymerization in the presence of varying levels of SepF. The stoichiometric SepF:FtsZ ratios are indicated for each curve. f Negatively stained EM micrographs of FtsZ filaments in the absence (left) and presence (right) of SepF. The polymers in the left-hand panel have a width of about 4 nm, which corresponds to the width of FtsZ. The bundles shown in the right-hand panel range in width from 20–60 nm. Scale bars are 150 nm. The data shown are representative of experiments made independently in triplicate. g SPR responses in resonance units (RU) for 200 μM FtsZ_CTD interacting with immobilized SepF (blue), SepF_F131A (red), and SepF_K125E/F131A (green). The detailed SPR results are shown in Supplementary Fig. 9. Source data are provided as a Source Data file.