Escherichia coli FtsZ polymers contain mostly GTP and have a high nucleotide turnover.
ABSTRACT The cell division protein FtsZ is a GTPase structurally related to tubulin and, like tubulin, it assembles in vitro into filaments, sheets and other structures. To study the roles that GTP binding and hydrolysis play in the dynamics of FtsZ polymerization, the nucleotide contents of FtsZ were measured under different polymerizing conditions using a nitrocellulose filter-binding assay, whereas polymerization of the protein was followed in parallel by light scattering. Unpolymerized FtsZ bound 1 mol of GTP mol(-1) protein monomer. At pH 7.5 and in the presence of Mg(2+) and K(+), there was a strong GTPase activity; most of the bound nucleotide was GTP during the first few minutes but, later, the amount of GTP decreased in parallel with depolymerization, whereas the total nucleotide contents remained invariant. These results show that the long FtsZ polymers formed in solution contain mostly GTP. Incorporation of nucleotides into the protein was very fast either when the label was introduced at the onset of the reaction or subsequently during polymerization. Molecular modelling of an FtsZ dimer showed the presence of a cleft between the two subunits maintaining the nucleotide binding site open to the medium. These results show that the FtsZ polymers are highly dynamic structures that quickly exchange the bound nucleotide, and this exchange can occur in all the subunits.
Full-textDOI: · Available from: Jesús Mingorance, May 29, 2015
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ABSTRACT: Cell division in bacteria takes place at the midcell and occurs after DNA has been duplicated and segregated into two nucleoids. The division process starts with the localization of FtsZ at the center of the cell and formation of a septal ring structure called Z-ring. Once the septum is fully formed, the Z-ring disappears and the daughter cells separate. An ordered assembly of other proteins follows this process (eg. FtsA, ZipA, FtsK, FtsQ, FtsL, FtsB, FtsW, FtsI, FtsN). FtsZ is a highly conserved protein that is found in most of the major groups of bacteria. FtsZ is a structural homolog of tubulin; like tubulin, purified FtsZ binds and hydrolyses GTP and assembles in vitro into filaments, sheets and other structures. One important inhibitory system, the Min system, is crucial for the precise positioning of the Z-ring. In E. coli this system consist of the FtsZ assembly inhibitor, MinC protein, and the MinD and MinE proteins which move from one cell pole to the other. Because MinC is associated with the relocating MinD protein, FtsZ assembly is inhibited at the cell poles. Another important regula- tory system is nucleoid occlusion. Like Min system, nucleoid occlusion negatively regulates Z-ring assembly. Acting independently of the Min system nucleoid occlusion prevents the assembly of the Z ring on top of unreplicated chromosomal DNA. Several positive and negative regulators of Z ring assembly are known eg. ZipA, EzrA, ClpX, SulA, Noc proteins. The lack of FtsA, ZipA and FtsN cell division proteins suggests that the mechanisms of cell division are likely to be different in Mycobacterium as compared with E. coli. FtsZ and FtsQ are essential cell division proteins in Mycobacterium smegmatis and M. tuberculosis. The C-termini of M. tuberculosis FtsZ and FtsW carries a string of amino acid residues that are absent in their E. coli counterparts. FtsZ and FtsW of M. tuberculosis are binding partners and that binding involves a cluster of aspartate residues in the C-tail of FtsZ.
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ABSTRACT: Together with ATP, the C-terminal region of the essential streptococcal FtsA protein acts as an intramolecular switch to promote its polymerization and attachment to the membrane. During septation, FtsA is known to anchor the constricting FtsZ ring and, subsequently, the divisome to the membrane. Truncation of the C terminus of the streptococcal FtsA (FtsADCt) facilitates a more rapid ATP-dependent polymerization in solution than is seen with the full-length protein (FtsA+). The FtsADCt polymers are more organized and compact than those formed in solution by FtsA+, resembling the shape of the membrane-associated FtsA+ polymers. We find that ATP, besides being needed for polymerization, is required for the attach- ment of FtsA+ to lipid monolayers and to vesicle membranes. We propose a model in which the binding of ATP activates a switch favoring the polymerization of FtsA and at the same time driving the amphipathic helix at its C terminus to become at- tached to the membrane. Conversely, when FtsA is in the cytoplasm, the C terminus is not engaged in the attachment to the membrane, and it obstructs polymerization. ATP-dependent polymerization of FtsA inside membrane vesicles causes vesicle shrinkage, suggesting that, besides providing a membrane attachment for FtsZ, the FtsA C terminus may also introduce local alterations in the membrane to facilitate septation.mBio 11/2014; 5(6):e02221-14. DOI:10.1128/mBio.02221-14 · 6.88 Impact Factor