The major outer membrane lipoprotein and new lipoproteins share a common signal peptidase that exists in the cytoplasmic membrane of Escherichia coli.

The cell envelope of Escherichia coli possesses several lipoproteins including the major outer membrane lipoprotein. These lipoproteins are synthesized as a signal peptide-carrying precursor that is subsequently modified with glyceride. In this work, lipoprotein signal peptidase that processes the precursor of the major lipoprotein was partially purified from cells harboring a plasmid that carries the gene for this enzyme (1spA). The enzyme was also active against the glyceride-containing precursors of the peptidoglycan-associated lipoprotein and many additional membrane lipoproteins. The unmodified precursor of the major lipoprotein was not attacked by the enzyme. The enzyme was exclusively localized in the cytoplasmic membrane.