The tubulin homolog FtsZ is the major cytoskeletal protein in bacterial cytokinesis. Our recent work has shown that FtsZ can reconstitute Z rings in liposomes, and these can generate a constriction force without any other proteins. FtsZ thus acts as cytoskeleton and motor all in one. Our work suggests that the constriction force is generated by a curved conformation of the FtsZ protofilaments (pfs) bending the membrane. We now propose to address three of the most important and immediate questions. (1) What is the structure of the Z ring in bacteria? There are two competing models. The "ribbon" model proposes that pfs are laterally associated to make a ribbon, and the "scattered" model proposes that the pfs are more widely scattered on the membrane and not in contact. We propose three imaging techniques to resolve this controversy: super-resolution light microscopy and two newly-developed EM probes. Resolving these models is essential to explore the physics of the constriction force. (2) What is the mechanism of pf dynamics? We have shown that FtsZ pfs are rapidly exchanging subunits, with a half time of 5-10 s. The mechanism could involve dynamic instability, treadmilling or fragmentation/annealing. We propose to image single pfs by super-resolution light microscopy and by cryo and negative stain EM to resolve the mechanism. (3) What is the structure of curved pfs? We have strong evidence that the constriction force is generated by pfs adopting a curved conformation that exerts a bending force on the membrane. However, there are structural contradictions that need to be resolved, especially regarding the orientation - is the C terminus on the inside or the outside of the curvature? To determine this orientation, we propose to develop FtsZ subunits with a large C-terminal tag visible by EM. Importantly, we now know that there are two curved conformations, the highly curved miniring, which is an analog of tubulin rings, and an intermediate curved form. We suspect these may have opposite orientations, and our tagged FtsZ should resolve this.
Our overall goal is to determine the mechanism by which bacteria divide. This is foremost an issue of basic science, to expand our knowledge of biology. It also has potential clinical relevance. FtsZ is highly conserved in bacteria, and is an attractiv target for new antibiotics. Several lead compounds targeting FtsZ are already being studied and developed.
|Milam, Sara L; Erickson, Harold P (2013) Rapid in vitro assembly of Caulobacter crescentus FtsZ protein at pH 6.5 and 7.2. J Biol Chem 288:23675-9|
|Gardner, Kiani A J Arkus; Moore, Desmond A; Erickson, Harold P (2013) The C-terminal linker of Escherichia coli FtsZ functions as an intrinsically disordered peptide. Mol Microbiol 89:264-75|
|Osawa, Masaki; Erickson, Harold P (2013) Liposome division by a simple bacterial division machinery. Proc Natl Acad Sci U S A 110:11000-4|
|Chen, Yaodong; Milam, Sara L; Erickson, Harold P (2012) SulA inhibits assembly of FtsZ by a simple sequestration mechanism. Biochemistry 51:3100-9|
|Osawa, Masaki; Erickson, Harold P (2011) Inside-out Z rings--constriction with and without GTP hydrolysis. Mol Microbiol 81:571-9|
|Chen, Yaodong; Erickson, Harold P (2011) Conformational changes of FtsZ reported by tryptophan mutants. Biochemistry 50:4675-84|
|Erickson, Harold P; Osawa, Masaki (2010) Cell division without FtsZ--a variety of redundant mechanisms. Mol Microbiol 78:267-70|
|Erickson, Harold P; Anderson, David E; Osawa, Masaki (2010) FtsZ in bacterial cytokinesis: cytoskeleton and force generator all in one. Microbiol Mol Biol Rev 74:504-28|
|Osawa, Masaki; Erickson, Harold P (2009) Chapter 1 - Tubular liposomes with variable permeability for reconstitution of FtsZ rings. Methods Enzymol 464:3-17|
|Osawa, Masaki; Anderson, David E; Erickson, Harold P (2009) Curved FtsZ protofilaments generate bending forces on liposome membranes. EMBO J 28:3476-84|
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