Mechanism of the septal membrane localization of bacterial lipid synthases

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We have found that cardiolipin-rich domains are localized in the septal region and at the poles of Bacillus subtilis membranes and further that phosphatidylethanolamine-rich domains and many lipid synthases are localized on septal region of the membranes. To understand the possible mechanism how the specific phospholipid-rich domains are generated and maintained and what their function may be, we started to examine the mechanism(s) how the lipid synthases are localized to the septal membranes. One approach is to clarify the interactions of the lipid synthases with the proteins and enzymes involved in cell division and also the interactions between the lipid synthases which are expected to form a large complex of the enzymes. Meanwhile we found the enzyme YneS that catalyzes the initial step of glycerophospholipid synthesis, which uses acylphosphate, a new acyl donor produced by PlsX. Hence, we focused on the new enzymes to found an interaction between the two. PlsX interacts with itself. No interaction was found with acyl carrier protein. The other approach is to reveal the region responsible for the septal localization within the enzymes. GFP-fused cardiolipin synthase and phosphatidylglycerophosphate synthase were used as representatives and a series of deletion derivatives were constructed to see the septal localization. Both representatives were found to have amphiphilic α helices at COOH-terminal, probably responsible for the septal localization. Transmembrane helices in phosphatidylglycerophosphate synthase were suggested to be responsible for the septal localization.