FtsZ Constriction Force – Curved Protofilaments Bending Membranes

Abstract

FtsZ assembles in vitro into protofilaments (pfs) that are one subunit thick and ~50 subunits long. In vivo these pfs assemble further into the Z ring, which, along with accessory division proteins, constricts to divide the cell. We have reconstituted Z rings in liposomes in vitro, using pure FtsZ that was modified with a membrane targeting sequence to directly bind the membrane. This FtsZ-mts assembled Z rings and constricted the liposomes without any accessory proteins. We proposed that the force for constriction was generated by a conformational change from straight to curved pfs. Evidence supporting this mechanism came from switching the membrane tether to the opposite side of the pf. These switched-tether pfs assembled “inside-out” Z rings, and squeezed the liposomes from the outside, as expected for the bending model. We propose three steps for the full process of cytokinesis: (a) pf bending generates a constriction force on the inner membrane, but the rigid peptidoglycan wall initially prevents any invagination; (b) downstream proteins associate to the Z ring and remodel the peptidoglycan, permitting it to follow the constricting FtsZ to a diameter of ~250 nm; the final steps of closure of the septum and membrane fusion are achieved by excess membrane synthesis and membrane fluctuations.

How bacterial cell division might cheat turgor pressure – a unified mechanism of septal division in Gram‐positive and Gram‐negative bacteria

“…The components are: FtsZ, a 5 nm diameter sphere with a 10 nm peptide linker that connects to FtsA, a 5 nm sphere with an amphipathic helix that inserts into the IM. The Z ring shown here in cross-section is a ribbon of four protofilaments, consistent with recent cryoEM [39]; see also [50] for arguments supporting this narrow width. The IM, a 4 nm thick lipid bilayer that defines the two sides of the septum ∼70 nm apart; PG parental, a 30 nm wide sheet represented as a blue to green gradient inside to outside; PG bridge, a thickening of the parental PG at the septum [33]; periplasm, the 20 nm space between the IM and PG; FtsI (PBP3 in E. coli and PBP2B in B. subtilis), a transmembrane protein with an elongated periplasmic domain [51] that can bridge the 10 nm wide periplasmic space in the septum.…”

Gain‐of‐function variants of FtsA form diverse oligomeric structures on lipids and enhance FtsZ protofilament bundling

“…The FtsZ ring focuses in a narrow band in order to successfully synthesize the division septum (Coltharp and Xiao, ). One focusing mechanism in E. coli likely involves FtsZ filament crosslinking or lateral interactions (Lan et al , ; Dajkovic et al , ; Milam et al , ; Szwedziak et al , ; Haeusser et al , ; Coltharp et al , ), the structures and potential roles of which were recently reviewed (Erickson and Osawa, ; Krupka and Margolin, ). It is likely that the extent of FtsZ bundling needs to be balanced, because FtsZ that bundles proficiently (as assayed in vitro ) can disrupt normal cell division as well as too little.…”

Functional Modules of Minimal Cell Division for Synthetic Biology

“…Right path of the flowchart: The challenge in the production of a module for replication and homogeneous distribution of genetic information in a synthetic container is shown in the right path. [81] However, these hypotheses still remain to be verified. The pole to pole separation of genetic information is ensured by a minimal segrosome (e.g., Par or Alp system).…”

“…[57] ZipA is integrated into the membrane via an N-terminal domain and also contains a C-terminal FtsZ-binding domain, both connected via a flexible linker. [76,[79][80][81] [76] FtsZ shows outstanding treadmilling dynamics in vivo as well as in vitro in circular polymer structures with a diameter of ≈1 µm.…”

“…[101] Due to its double fatty acid tail, cardiolipin prefers high-curvature, rather than flat, bilayer structures, implying that a locally increased prevalence might favor morphological transformations via mechanical destabilization, thereby supporting division. [81] However, further studies on the controlled manipulation of membrane compositions are needed to elucidate the connection between proper cell division and spatial confinement. [57] Furthermore, it has been shown that MinD is preferentially binding to anionic phospholipids on the inner membrane.…”