Structural insights into the activation of the divisome complex FtsWIQLB

Abstract

Cell division is a fundamental process for the growth and reproduction of organisms. Most bacteria proliferate through binary fission, which occurs by the ingrowth of the cell membrane and the peptidoglycan (PG) cell wall to form a septum at midcell 1 . The synthesis of the septal PG is catalyzed by a multi-protein complex named divisome, containing the core components PG glycosyltransferase (GT) FtsW and PG transpeptidase (TP) FtsI that are responsible for septal glycan chain polymerization and crosslinking, respectively 2 , 3 (Fig. 1a ). The action of the septal PG synthase FtsWI is strictly regulated by divisome regulatory proteins, including FtsN, FtsA, FtsEX, and FtsQLB 4 , 5 , 6 , 7 . Previous mutagenic studies suggest that FtsN initiates a signaling cascade for FtsWI activation through FtsQLB 8 , 9 . However, the mechanism by which FtsWI is activated is not fully understood. Here, we determined a cryo-EM structure of FtsWI bound to the regulatory proteins FtsQLB at 3.3 Å and performed mutagenic studies to reveal the molecular details for understanding the mechanism of divisome activation. Fig. 1: Structural characterization of the Pa FtsWIQLB complex. a Schematic diagram of peptidoglycan synthesis by the divisome complex FtsWIQLB. b Topology of FtsW, FtsI, FtsL, FtsB, and FtsQ. c , d Cryo-EM map ( c ) and structure ( d ) of the Pa FtsWIQLB complex. Flexible loops are shown as dashed lines. e Transmembrane helices of FtsW from the side and top views, showing ECL4 (grey). f The conserved residues present in the central cavity of FstW (corresponding residues in E. coli are in parentheses). g Cell viability and microscopic phenotypes of FtsW variants with mutated cavity residues. h Structural superimposition of Pa FtsW-FtsI and Tt RodA-PBP2 (PDB:6PL5) with overlapped FtsW and RodA as reference. i The interactions between FtsW and FtsL. j The putative catalytic residue D275 of FtsW interacts with residues within the central cavity. k – n Interactions between components of the FtsWIQLB complex are highlighted in boxes. Hydrogen bonds and salt bridges are indicated with yellow or black dashed lines. Full size image

Topics & Concepts