Abstract
We have used a simple model system to test the prediction that surface attachment strength of filaments presenting a torsion would affect their shape and properties. FtsZ from E. coli containing one cysteine in position 2 was covalently attached to a lipid bilayer containing maleimide lipids either in their head group (to simulate tight attachment) or at the end of a polyethylene glycol molecule attached to the head group (to simulate loose binding). We found that filaments tightly attached grew straight, growing from both ends, until they formed a two-dimensional lattice. Further monomer additions to their sides generated a dense layer of oriented filaments that fully covered the lipid membrane. After this point the surface became unstable and the bilayer detached from the surface. Filaments with a loose binding were initially curved and later evolved into straight thicker bundles that destabilized the membrane after reaching a certain surface density. Previously described theoretical models of FtsZ filament assembly on surfaces that include lateral interactions, spontaneous curvature, torsion, anchoring to the membrane, relative geometry of the surface and the filament ‘living-polymer’ condition in the presence of guanosine triphosphate (GTP) can offer some clues about the driving forces inducing these filament rearrangements.
Highlights
FtsZ is a bacterial cytoskeletal protein that binds and hydrolyzes guanosine triphosphate (GTP) to self-aggregate into dynamic filaments and guide the assembly of the septal ring on the inner side of the membrane at midcell that constricts the cell during division
FtsZ is conserved throughout bacteria, both gram-positive and gram-negative, archaea [1] and exists in chloroplasts and in the mitochondria of certain eukaryotes [2]
Ever since its discovery near 25 years ago, its great polymorphism and dynamic behavior have raised many questions regarding how such a dynamic and polymorphic structure can be responsible for force generation [3,4]
Summary
FtsZ is a bacterial cytoskeletal protein that binds and hydrolyzes GTP to self-aggregate into dynamic filaments and guide the assembly of the septal ring on the inner side of the membrane at midcell that constricts the cell during division. Strategies to artificially attach and orient FtsZ to membranes have provided useful information about structural and dynamic properties of the filaments [26,27,28] Even if these results obtained in model systems cannot be directly extrapolated to the more complex behavior in vivo in the presence of other modulating proteins, they have been extremely useful to reveal intrinsic properties of the filaments. The results serve to illustrate the impact of the surface attachment on FtsZ filament behavior and can shed some light on the potential function of being attached to the membrane atphprorouxgihmaatfelelyxib18le0lidnekgerre.es from the C-terminal domain through which the proteins are attached in vivo. The other lipid used contains the maleimide moiety at the end of a PEG spacer (2000 MW), to simulate a looser binding (Figure 1)
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