Bidirectional FtsZ filament treadmilling transforms lipid membranes via torsional stress

Abstract

FtsZ is a key component in bacterial cell division, being the primary protein of the presumably contractile Z ring. Reconstituted in vitro, it shows two distinctive features that could so far however not be mechanistically linked: self-organization into directionally treadmilling vortices on solid supported membranes, and shape deformation of flexible liposomes. In cells, circumferential treadmilling of FtsZ was shown to recruit septum-building enzymes, but an active force production remains elusive. To determine direct contributions of FtsZ to membrane constriction, we designed a novel in vitro assay based on soft lipid tubes pulled from FtsZ decorated giant lipid vesicles (GUVs) by optical tweezers. FtsZ actively transformed these tubes into spring-like structures, where GTPase activity promoted spring compression. Operating the optical tweezers in lateral vibration mode and assigning spring constants to FtsZ coated tubes, we found that that FtsZ indeed exerts pN forces upon GTP hydrolysis, through torsional stress induced by bidirectional treadmilling.

Essential dynamic interdependence of FtsZ and SepF for Z-ring and septum formation in Corynebacterium glutamicum

“…Protein dynamics are intrinsic functional features of tubulin (dynamic instability 44 ) and FtsZ (treadmilling 10 ). FtsZ by itself has the properties not only to self-organize and provide directionality, but also to deform lipids when a membrane-binding motif is attached to the protein [45][46][47] . In this case, FtsZ has been shown to assemble into dynamic vortices in vitro without the need for accessory proteins, but critically relying on concentration thresholds 46 .…”

FtsZ Reorganization Facilitates Deformation of Giant Vesicles in Microfluidic Traps**

“…Strikingly, this shape change was accompanied by FtsZ filament reorganization: elongated FtsZ filaments re-polymerized into ring-like structures (Figure 2 d, i-ii). Although our image resolution is insufficient to discern filament organization, the dimensions make it likely that these structures correspond to the dynamic rings previously described (see Figure S9 for experiments under identical conditions to [23] ). These ring-like filaments formed in short cone-like membrane protrusions at GUV surfaces, as soon as the mechanical membrane tension was decreased upon isosmotic GUV release from the traps (s mec (shape change) = À70 AE 10 mN m À1 ; n(GUV) = 10, Figure 2 e-f, Figure S8b; see SI for details on calculation of s mec from Figure S6 data).…”

Essential dynamic interdependence of FtsZ and SepF for Z-ring and septum formation inCorynebacterium glutamicum

“…FtsZ by itself has the properties not only to self-organise and provide directionality, but also to deform lipids when a membrane binding motif is attached to the protein [40][41][42] . In this case, FtsZ has been shown to assemble into dynamic vortices in vitro without the need for accessory proteins such as FtsA, but critically relying on concentration thresholds 41 .…”