The assembly of essential proteins occurs in two steps FtsZ, FtsA, ZipA, Zap proteins (AвЂ“E) and FtsEX assemble early at the future division site, before any constriction is visible. coli, cell division involves over 30 proteins, with twelve of these (the Fts proteins and ZipA) absolutely required for the process ( Margolin, 2005). coli, which will be the focus of this article. These have been observed in several species including, but not limited to, the Gram-positive Bacillus subtilis, Staphylococcus aureus and Streptococcus pneumoniae and the Gram-negative Caulobacter crescentus and E. Genetic and biochemical data have demonstrated many proteinвЂ“protein interactions between various peptidoglycan synthases, hydrolases, regulatory proteins, and cytoskeletal elements (reviewed in Typas et al., 2012 Egan and Vollmer, 2013). Subsequent experimental evidence supported the multi-enzyme complex hypothesis. What are the molecular mechanisms of sacculus growth? HГ¶ltje (1998) proposed that multi-enzyme complexes made of peptidoglycan synthases and hydrolases simultaneously synthesize new peptidoglycan and incorporate it into the sacculus, and remove old material, by a so-called 3-for-1 mechanism.

coli is accompanied by the release of as much as 50% of the total peptidoglycan material per generation by hydrolases ( Goodell, 1985). Remarkably, the growth of the single-layered sacculus in E. Sacculus growth has to be well-controlled, because the accumulation of defects may lead to cell lysis this is the case when antibiotics like ОІ-lactams inhibit peptidoglycan synthesis.

Thus, a bacterial cell needs to increase the surface of its sacculus in order to grow and divide. Peptidoglycan (PG) forms a net-like, continuous layer, called the sacculus, surrounding the cytoplasmic membrane. The peptidoglycan cell wall is an essential component of most bacteria, required for the maintenance of cell morphology and structural integrity ( Weidel and Pelzer, 1964). From this hypothesis we infer a possible mechanism for peptidoglycan synthesis during division. Based on this principle we present a hypothesis for the stoichiometry of the core of the divisome, taking into account known proteinвЂ“protein interactions. Interestingly, they observed that most proteins which participate in known multiprotein complexes are synthesized proportional to their stoichiometry. A recent study ( Li et al., 2014) used ribosome profiling to measure the absolute protein synthesis rates in E. However, little is known about the nature of the interactions involved and the stoichiometry of the proteins within the divisome. Although the precise function of most divisome proteins is unknown, it became apparent in recent years that dynamic proteinвЂ“protein interactions are essential for divisome assembly and function. For this, more than 30 proteins localize to mid-cell where they form a large, ring-like assembly, the divisome, facilitating division.

The Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, UKДividing Escherichia coli cells simultaneously constrict the inner membrane, peptidoglycan layer, and outer membrane to synthesize the new poles of the daughter cells.

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