Block of alkaline phosphatase processing due to single amino acid substitutions affects phospholipid content and turnover in E. coli cells secreting the mutant proteins

Amino acid substitutions in the signal peptide cleavage site of E. coli alkaline phosphatase (Val for Ala(-1) or Pro for Arg(+1)) impair the enzyme processing and anchoring of precursors in the cytoplasmic membrane. In cells secreting these mutant proteins the relative content and the rate of turnover of anionic phospholipids (phosphatidylglycerol and cardiolipin) are increased. The increase in the transfer of phosphoglycerol residues from phosphatidylglycerol to periplasmic membrane-derived oligosaccharides or to the model substrate arbutin, performed by phosphoglycerol transferase I, indicates increased content of phosphatidylglycerol on the outer side of the cytoplasmic membrane. These results suggest an interaction of phosphatidylglycerol with the alkaline phosphatase precursor followed by their joint translocation across the cytoplasmic membrane of E. coli.