Apparent cooperative assembly of the bacterial cell division protein FtsZ demonstrated by isothermal titration calorimetry.
The assembly dynamics of FtsZ, a prokaryotic homolog of tubulin, are important for their role in bacterial cytokinesis. Here we used isothermal titration calorimetry (ITC) to measure the heat of FtsZ self-association under various conditions. The measurements were designed to test whether FtsZ protofilaments are assembled by an isodesmic (linear aggregates in which each bond has an identical equilibrium constant) or a cooperative (aggregates only become stable after forming a oligomeric nucleus) assembly process. The isodesmic model can fit the assembly in GDP closely but cannot fit the assembly in GTP. FtsZ-GTP without Mg(2+) exhibits an apparent critical concentration, which is indicative of cooperative assembly, near 2.9 microm. With 2.5 mm Mg(2+) (which allows FtsZ to hydrolyze GTP) the critical concentration is reduced 10-fold to approximately 0.31 microm. Both with and without Mg(2+) there is no evidence for assembly below the critical concentration, but there is an abrupt transition to full assembly above. The ITC data are highly suggestive of a cooperative assembly, although this is difficult to reconcile with the 1-subunit-thick protofilaments observed by electron microscopy.
Caplan
Michael R
MR
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Erickson
Harold P
HP
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001671:Biochemistry / Q000379:methods; D002151:Calorimetry; D002455:Cell Division; D003598:Cytoskeletal Proteins; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008854:Microscopy, Electron; D013816:Thermodynamics; D013997:Time Factors
D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D008274:Magnesium