ABNORMAL FRACTIONATION OF BETA-LACTAMASE IN ESCHERICHIA-COLI - EVIDENCE FOR AN INTERACTION WITH THE INNER MEMBRANE IN THE ABSENCE OF A LEADER PEPTIDE

Beta-Lactamase with the - 20 to - 1 region of the leader peptide deleted (almost complete deletion of the leader peptide) [DELTA(-20,-1) beta-lactamase] was released from Escherichia coli cells by osmotic shock. Fractionation of the cells by conversion to spheroplasts and protease accessibility experiments further indicated that a portion of the protein may be bound to the cytoplasmic membrane and be partially exposed in the periplasmic space. Expression of DELTA(-20,-1) beta-lactamase conferred a 25-fold increase in the 50% lethal dose for amplicillin relative to that for controls, thus confirming that a small amount (about 2%) of the active protein is completely exported form the cytoplasm. These results suggest that even in the absence of a leader peptide, mature beta-lactamase is able to interact with the cytoplasmic membrane and be translocated into the periplasmic space, albeit with a low efficiency.