Depletion of phosphatidylethanolamine, the major membrane phospholipid of Escherichia coli, depresses post-translocational modification of alkaline phosphatase in the periplasm

Unbalanced phospholipid composition due to depletion of the major phospholipid of Escherichia coli, phosphatidylethanolamine, was shown previously to significantly decrease the secretion and transcriptional expression of periplasmic alkaline phosphatase of this bacterium. The current work studies the effect of this unbalance on post-translocational proteolytic modification of the enzyme, proceeding in the periplasm with the formation of its isoforms. It has been revealed that under phosphatidylethanolamine depletion the content of incompletely modified (intermediate) isoforms I and II increases. This increase does not depend on the level of enzyme synthesis and the mechanism of its regulation (expression of the chromosomal gene or the gene cloned in plasmid under the control of the endogenous promoter PPHO or exogenous promoter PBAD). Depression of post-translocational modification of alkaline phosphatase in phosphatidylethanolamine-depleted cells is supposed to be a result of the lower efficiency of secretion of modifying proteinase (product of the iap gene) localized, like alkaline phosphatase, in the periplasm of Escherichia coli.