Fig. 1: The FtsB-FtsL-FtsQ (FtsBLQ) complex in the bacterial divisome and its overall structure.

a A schematic view of the recruitment of FtsBLQ to the divisome in E. coli. Divisome proteins are shown as circles: FtsB (blue); FtsL (pink); FtsQ (yellow); the upstream (black) and downstream (white) proteins of FtsBLQ. The inner and outer membranes and the periplasm are shown in grey, light blue, and orange layers. b A cartoon model of the molecular relationship between key divisome proteins at the division site: FtsBLQ (blue, pink, and yellow), FtsK (only TM domain shown, wheat), PBP1b (green), FtsW-FtsI (cyan and purple), FtsN (grey) and FtsA (orange). Solid black arrows/lines indicate the activating/inhibitory regulations. Dashed lines with arrows indicate the recruitment. The inner membrane (IM) is drawn as a grey lipid bilayer, and peptidoglycan (PG) sugars as hexagons. c Overall structure of the FtsBLQ complex as an inverted “V” shape, showing FtsB (blue), FtsL (pink), and FtsQ (yellow) in a stoichiometry of 1:1:1, with each domain accordingly labeled. All secondary structural elements are numbered sequentially. Missing stretches of residues, including residues 90–103 of FtsB; 1–39 of FtsL; 1–21, and 259–276 of FtsQ, are drawn as dashed lines. d Domain organization of FtsB, FtsL, and FtsQ with dash lines indicating the observed interactions between each other within the complex. The TM, the coiled coil, the interaction sites, the N- and C- termini, and the start and end of each structure element are also labeled. e The length difference between the periplasmic parts of FtsBL and FtsQ is shown in the same view as (c) - left or rotated for 90° - right. f The tilted FtsBLQ structure that fits all TM domains in the membrane, in the same views as in (e). In c–f the new FtsB-FtsQ interface is highlighted with an orange star.