Non-bilayer lipids stimulate the activity of the reconstituted bacterial protein translocase

To determine the phospholipid requirement of the preprotein translocase in vitro, the Escherichia coil SecYEG complex was purified in a delipidated fo rm using the detergent dodecyl maltoside, SecYEG was reconstituted into lip osomes composed of defined synthetic phospholipids, and proteoliposomes wer e analyzed for their preprotein translocation and SecA translocation ATPase activity. The activity strictly required the presence of anionic phospholi pids, whereas the non-bilayer lipid phosphatidylethanolamine was found stim ulatory. The latter effect could also be induced by dioleoylglycerol, a lip id that adopts a non-bilayer conformation, Phosphatidylethanolamine derivat ives that prefer the bilayer state were unable to stimulate translocation, In the absence of SecG, activity was reduced, but the phospholipid requirem ent was unaltered. Remarkably, nonbilayer lipids were found essential for t he activity of the Bacillus subtilis SecYEG complex. Optimal activity requi red a mixture of anionic and non-bilayer Lipids at concentrations that corr espond to concentrations found in the natural membrane.