A DUAL ROLE FOR PHOSPHATIDYLGLYCEROL IN PROTEIN TRANSLOCATION ACROSS THE ESCHERICHIA-COLI INNER MEMBRANE

The involvement of phosphatidylglycerol in the SecA-independent transl ocation of M13 procoat in Escherichia coli was demonstrated. Processin g of procoat to mature coat protein was retarded when the level of pho sphatidylglycerol was reduced. In vitro translocation experiments usin g inner membrane vesicles isolated from a strain with inducible synthe sis of phosphatidylglycerol, showed that translocation of procoat and of a SecA-dependent procoat analog was proportional to the content of phosphatidylglycerol. Moreover, introduction of phosphatidylglycerol b y means of a lipid transfer method into phosphatidylglycerol-depleted inner membrane vesicles, efficiently restored procoat translocation. T he phosphatidylglycerol dependence in both the SecA-dependent and -ind ependent translocation pathway indicates that phosphatidylglycerol pla ys a dual role in translocation. We suggest that besides membrane bind ing of SecA this lipid has a direct interaction with the M13 procoat i n translocation across the inner membrane.