Purification and characterization of a signal peptide, a product of protein secretion across the cytoplasmic membrane of Escherichia coli

A signal peptide, a processing product of the precursor of the lipoprotein in the cytoplasmic membrane of Escherichia coli, has been purified through extractions with butanol and ethyl ether and chromatographies with a Sephadex LH-60 column and Sep-pak C18. Analysis of the amino acid composition and sequencing of the N- and C-termini indicate that the signal peptide was intact, suggesting that the first step of the signal peptide catabolism in the cytoplasmic membrane is the cleavage of the intact signal peptide. During the purification, the signal peptide exhibited unique features, including strong interaction with phospholipids. The possible importance of such features in the process of protein translocation across membranes is discussed.