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Fig. 1 (a) Scheme of the divisome complex showing key subunits. Early assembly proteins (light gray) are recruited to the midcell plane first. FtsA and ZipA anchor FtsZ protofilaments on the inner membrane. FtsZ is a prokaryotic tubulin homologue and forms a ring at the nascent division site, the so-called Z ring, during cell division. This ring serves as a platform for the peptidoglycan synthesis machinery.45 FtsK is recruited to assist in chromosome segregation and in turn recruits the FtsQBL complex, which serves as a structural hub for recruitment of late assembly proteins (dark gray). Interaction of FtsN with the FtsQBL complex indicates the completion of divisome complex formation.11,12 (b) Crystal structure (PDB: 6h9o) of periplasmic FtsQ domains (white) in a complex with FtsB-derived peptide 24 (blue). FtsB residues essential for binding are shown in a stick representation.23 (c) Top: sequence of peptide 24-derived macrocycles including associated secondary structure elements in the FtsQ-bound state. Bottom: synthesis sketch of macrocyclic peptides. (d) Fluorescence polarization (FP) measurements using fluorescein-labeled analogues of 24 (c = 10 nM) and FtsQ(50?276) (c = 0.06 nM?100 ?M). The table provides KD-values for macrocyclic peptides bound to FtsQ(50?276). Peptide cross-link lengths are indicated (6?13 carbon atoms; for peptide details, see Table S1). All measurements were performed in triplicate (n = 3 replicates, error bars = SD).