Map-CellDiv

A major challenge in microbiology concerns the nature of the mechanisms of cell division. This process requires a myriad of protein–protein interactions, the coordination of a remarkable suite of strategies and competing biochemical reactions. In most bacteria, cell division results in the formation of two genetically and morphologically identical daughter cells. Such binary fission process first requires the identification of the cell middle followed by the recruitment of the division machinery, which first component is the highly conserved tubulin-like protein FtsZ. FtsZ forms a ring that eventually constricts to give rise to two newborn cells. A long-standing question was thus how bacterial find their middle to select the site of cell division. To date, most of our knowledge of bacterial cell division and morphogenesis comes from studies on a few bacterial models and notably Escherichia coli and Bacillus subtilis. However, these two rod-shaped bacteria are actually not representative of the diversity of existing bacterial cell shape, mode of growth and developmental behavior. In addition, the systems identified in Escherichia coli and Bacillus subtilis, that prevent the assembly of the division machinery near the cell pole or over the chromosome are not found in a large array of bacteria. Last, there are several lines of evidence that these systems are not sufficient per se for the identification of the cell center. Collectively, it came thus has no surprised that other proteins have been found to participate in the positioning of the division site at mid-cell. This is the case in some proteobacteria and actinobacteria. In the ongoing efforts to determine what does identify the division site, we have recently uncovered an unprecedented mechanism in the bacterium Streptococcus pneumoniae. The key player of this system is a protein of unknown function that we named MapZ and that is conserved among streptococci and lactococci and most enterococci. We have shown that MapZ localizes at the division site before FtsZ to guide septum positioning. We found that MapZ moves apart as the cell elongates, therefore behaving as a permanent beacon of division sites. MapZ positioning at the future division site relies on the synthesis of the cell wall that mechanically pushes MapZ rings. MapZ then positions the FtsZ ring through direct protein-protein interactions. Further, we have found that MapZ phosphorylation is required for proper FtsZ ring formation and dynamics. The aim of this project is to determine at the molecular and cellular level how MapZ positions at midcell and how it controls the constriction of the FtsZ ring. To achieve our goals, we will use multidisciplinary and complementary approaches combining molecular genetics, proteomics, structural biology and cutting-edge live cell imaging techniques of different resolution and scale. This strategy will allow to track and measure the dynamic localization of MapZ and its partners and to give and integrated vision of the regulatory mechanism mediated by MapZ. The work is divided in three main tasks dedicated to (i) the structural features of the MapZ extracellular domain and mode of interaction with the cell wall, (ii) the characterization of MapZ partners in the cell division and cell wall synthesis machineries and the impact of MapZ on their localization and iii) the understanding of how MapZ phosphorylation influences the closure of the FtsZ ring. The outcomes of this project will allow deciphering a mechanism that is at odds with model regulatory systems of bacterial cell division and will contribute to the fundamental knowledge in life sciences. Streptococcus pneumoniae being an important human pathogens, one can even anticipate that our data could serve as a fundamental basis for future studies aiming at developing strategies to combat bacterial infectious diseases.