Divisome


The divisome is a protein complex in bacteria that is responsible for cell division, constriction of inner and outer membranes during division, and peptidoglycan synthesis at the division site. The divisome is a membrane protein complex with proteins on both sides of the cytoplasmic membrane. In gram-negative cells it is located in the inner membrane. The divisome is nearly ubiquitous in bacteria although its composition may vary between species.
The elongasome is a modified version of the divisome, without the membrane-constricting FtsZ-ring and its associated machinery. The elongasome is present only in non-spherical bacteria and directs lateral insertion of PG along the long axis of the cell, thus allowing cylindrical growth.

History

Some of the first cell-division genes of Escherichia coli were discovered by François Jacob's group in France in the 1960s. They were called fts genes, because mutants of these genes conferred a filamentous temperature-sensitive phenotype. At the non-permissive temperature, fts mutant cells continue to elongate without dividing, forming filaments that can be up to 150 m long. Two breakthroughs came with the discovery of the ftsZ gene in 1980 and the realization that the FtsZ protein was localized to the division plane of dividing cells. Several other fts genes, such as ftsA, ftsW, ftsQ, ftsI, ftsL, ftsK, ftsN, and ftsB, were all found to be essential for cell division and to associate with the divisome complex and the FtsZ ring. FtsA protein binds directly to FtsZ in the cytoplasm, and FtsB, FtsL and FtsQ form an essential membrane-embedded subcomplex. FtsK and FtsW are larger proteins with multiple transmembrane domains. FtsI, also known as PBP3, is the divisome-specific transpeptidase required for synthesis of the division septum.