PHOSPHATIDYLGLYCEROL DEPENDENT PROTEIN TRANSLOCATION ACROSS THE ESCHERICHIA-COLI INNER MEMBRANE IS INHIBITED BY THE ANTICANCER DRUG DOXORUBICIN - EVIDENCE FOR AN ELECTROSTATIC INTERACTION BETWEEN THE SIGNAL SEQUENCE AND PHOSPHATIDYLGLYCEROL

OmpF-Lpp, a model secretory protein, requires both a positively charge d signal sequence and phosphatidylglycerol (PG) for efficient transloc ation across the E coli inner membrane. Modification of the signal seq uence can, however, remove both these prerequisites for translocation providing OmpF-Lpp mutants which undergo either PG and charge dependen t or PG and charge independent translocation. Here we show that positi vely charged membrane interactive compounds (polylysine & doxorubicin) are able to inhibit PG dependent translocation of the OmpF-Lpp signal sequence mutants but not PG independent translocation. Doxorubicin is also shown to bind more efficiently to liposomes containing increased levels of anionic lipid indicating that in these assays it may be inh ibiting translocation by preventing electrostatic interaction between the anionic lipid head group and the positively charged signal sequenc es.