FtsZ and the division of prokaryotic cells and organelles

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Abstract
FtsZ is required for the formation of a ring structure, known as the Z ring, at the site of cell or organelle division. Contraction of the Z ring leads to fission of the cell or organelle. The FtsZ family of proteins is widely conserved among prokaryotes and plants where it is used in chloroplast division. However, FtsZ is notably absent in a branch of the archaea, several branches of bacteria and in the mitochondria of most eukaryotes. FtsZ is a structural homologue of tubulin, and its biochemical properties also resemble those of tubulins, including its ability to bind and hydrolyse GTP and assemble into protofilaments. Unlike tubulin, however, FtsZ does not form microtubules, and the precise nature of FtsZ-containing macromolecules in vivo is not known. The Z ring localizes to the centre of Escherichia coli cells at the correct time during the cell cycle. There has been much progress in understanding how two negative regulatory systems ensure the proper spatial regulation of the Z ring. Several regulators of Z-ring assembly have been discovered that might interact with the spatial and temporal regulatory network. Whereas the requirement of FtsZ in cytokinesis is well-established, it is unclear whether the Z ring drives cytokinesis actively by mechanical pulling against the membrane or more passively by the recruitment of cell-wall-synthesis enzymes, or both. Recent evidence indicates that a significant proportion of the FtsZ protein population is not ring associated, and that these proteins might have additional functions besides cytokinesis, such as the maintenance of cell shape. Good progress has been made in understanding the important role of FtsZ in the fission of organelles, particularly in chloroplasts. FtsZ proteins work along with dynamin and other components to divide organelles.