| Summary: | All life demands the temporal and spatial control of essential biological functions. However, the understanding of cellular organization in the prokaryotic kingdom is poorly understood. Bacteria lack many of the known organisers as well as the compartmentalisation of eukaryotic cells and have to count on the cell wall and the membrane as anchoring sites for fundamental processes. A novel supramolecular localisation pattern was found in the membrane of the apparently spherical bacterium Staphylococcus aureus. The phospholipid synthesis enzymes PlsY and CdsA are localised in a punctate pattern, along with a septal localisation in cells that are undergoing cell-division. This localisation pattern is stabilised by the cytoskeletal and cell-division-associated protein MreD. MreD, which is also localised in punctate pattern, is required for growth at 42°C. Cells lacking MreD stop growing and exhibit severe morphological defects along with the delocalisation of FtsZ. This phenotype might be explained by a decrease in cardiolipin levels which was revealed by thin layer chromatography and could be relieved by the addition of high amounts of NaCl to the growth medium. Fluorescence microscopy studies revealed similar localisation patterns as seen for PlsY for membrane proteins involved in phospholipid biosynthesis and other metabolic processes, but not for the secretion protein SecY. A novel protein-interaction system based on Förster Resonance Energy Transfer was established in S. aureus and used to demonstrate the interaction of PlsY with CdsA, MreD and PgsA (another phospholipid synthesis enzyme) suggesting the formation of phospholipid synthesis clusters in the membrane that would allow metabolic channelling. The observed localisation pattern is independent of wall teichoic acids, cardiolipin, lysinylated phosphatidylglycerolphosphate, squalene and peptidoglycan. However, PlsY has been found to localise homogeneously in the membrane when cells are treated with the FtsZ-polymerisation inhibitor PC190723 suggesting a potential role for FtsZ in the punctate patterned distribution of PlsY. This study illustrates a novel supramolecular structure of membrane proteins in S. aureus which could be a common feature across biology.
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