The way in which bacteria divide in order to grow is a highly-coordinated process and requires a complex choreography of many proteins, working inside and outside the cell membrane. Many of these proteins have a functional relationship with the synthesis and coordination of the external cell shape determining polymer called peptidoglycan (PG). This polymer provides a structural scaffold for many cellular processes as well as mechanical strength and protection, which requires modification during the process of cell division. A critical point occurs during cell division when the "old" cell wall PG must be degraded to allow separation of newly synthesized cells and this function is provided by a variety of PG hydrolases associated with the cell division FtsE-FtsX protein complex. At Warwick we have recently contributed to a new understanding of how this process occurs in rod shaped, gram negative bacteria. However, the situation in respiratory infection associated, ovoid-shaped gram positive bacterial pathogens, including Streptococcus pneumoniae is unclear at present. Notably there is a direct interaction and functionally essential interaction between FtsEX and a single specific PG hydrolase called PcsB making it an attractive extracellular target to prevent pneumococcal disease. In this proposal we directly address questions concerning a particular essential enzyme and the complex it makes with cell division proteins in Streptococcus pneumoniae. The cell division proteins FtsE and FtsX form a complex together that spans the bacterial membrane and anchors an extracellular enzyme called PcsB that is required for cell division. The binding and hydrolysis of ATP inside the cell by FtsE is transmitted through its membrane anchor partner protein FtsX and results in a major conformational shape change in PcsB outside the cell which controls its ability to cut the peptidoglycan layer and allow cell division. Building on new structural data and models, genetic constructs, biochemical data, assays and international collaboration, the goal of this proposal is to understand the role of PcsB in complex with FtsEX and elucidate the molecular events linking cell division with PG degradative enzymes required for growth and division in S. pneumoniae. Drugs or vaccines that interfere with this process could prevent division and could provide routes to new treatments for pneumococcal and related infectious disease. The research proposed in this grant proposal forms part of an international effort with colleagues in the US and Singapore to combat this problem. The scientific principles that we will reveal may also have application in other, related bacterial species. Our work leading to this application, provides computer simulations, microbiological tools, techniques and biochemical approaches that can now be applied to the key biological questions of how are these proteins controlled, how do they function and how we might interfere with this this process to provide future antimicrobial strategies for human or animal health.