Discovery of a bifunctional cardiolipin/phosphatidylethanolamine synthase in bacteria

Summary Phosphatidylethanolamine ( PE ) and cardiolipin ( CL ) are major components of bacterial and eukaryotic membranes. In bacteria, synthesis of PE usually occurs via decarboxylation of phosphatidylserine ( PS ) by PS decarboxylases ( Psd ). CL is produced by various CL synthases ( Cls ). Membranes of the plant pathogen X anthomonas campestris predominantly contain PE , phosphatidylglycerol ( PG ) and CL . The X . campestris genome encodes one Psd and six putative CL s. Deletion of psd resulted in loss of PE and accumulation of PS . The mutant was severely affected in growth and cell size. PE synthesis, growth and cell division were partially restored when cells were supplied with ethanolamine ( EA ) suggesting a previously unknown PE synthase activity. Via mutagenesis, we identified a Cls enzyme ( Xc _0186) responsible for EA ‐dependent PE biosynthesis. X anthomonas lacking xc_0186 not only lost its ability to utilize EA for PE synthesis but also produced less CL suggesting a bifunctional enzyme. Recombinant Xc _0186 in E . coli and in cell‐free extracts uses cytidine diphosphate diacylglycerol ( CDP‐DAG ) and PG for CL synthesis. It is also able to use CDP‐DAG and EA for PE synthesis. Owing to its dual function in CL and PE production, we consider Xc _0186 the founding member of a new class of enzymes called CL / PE synthase ( CL / PEs ).