Journal
EMBO JOURNAL
Volume 26, Issue 22, Pages 4694-4708Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/sj.emboj.7601895
Keywords
bacterial cytoskeleton; cell division; cryoelectron microscopy; FtsZ; tomography
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Funding
- NIAID NIH HHS [R01 AI067548] Funding Source: Medline
- NIGMS NIH HHS [R01 GM051986, R01 GM51986] Funding Source: Medline
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In prokaryotes, FtsZ (the filamentous temperature sensitive protein Z) is a nearly ubiquitous GTPase that localizes in a ring at the leading edge of constricting plasma membranes during cell division. Here we report electron cryotomographic reconstructions of dividing Caulobacter crescentus cells wherein individual arc-like filaments were resolved just underneath the inner membrane at constriction sites. The filaments' position, orientation, time of appearance, and resistance to A22 all suggested that they were FtsZ. Predictable changes in the number, length, and distribution of filaments in cells where the expression levels and stability of FtsZ were altered supported that conclusion. In contrast to the thick, closed-ring-like structure suggested by fluorescence light microscopy, throughout the constriction process the Z-ring was seen here to consist of just a few short (similar to 100 nm) filaments spaced erratically near the division site. Additional densities connecting filaments to the cell wall, occasional straight segments, and abrupt kinks were also seen. An `iterative pinching' model is proposed wherein FtsZ itself generates the force that constricts the membrane in a GTP-hydrolysis-driven cycle of polymerization, membrane attachment, conformational change, depolymerization, and nucleotide exchange.
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