Lipid and peptide specificities in signal peptide-lipid interactions in model membranes

Abstract

The present data show the critical importance of the anionic lipid content in monomolecular layers for the interaction with PhoE signal peptide. At 37°C and 100 mM NaCl the interaction is maximal at 30–40 mol% anionic lipid. The results correlate with the reduced translocation competence of Escherichia coli strain HD3122, which has a much lower anionic lipid content as compared to the wild- type strain SD12 (De Vrije et al. (1988) Nature 334, 173–175). PhoE signal peptide analogs as N- formyl PhoE signal peptide, PhoE signal peptide +(1–7) and PhoE signal peptide Val −8 → Trp −8 show the same lipid preference as PhoE signal peptide. On the other hand the affinity for an anionic lipid interface is strongly reduced for PhoE signal peptide Lys −19,−20 → Asp −19,−20 , which correlates with the less efficient translocation of PhoE protein carrying this signal sequence. At limiting anionic lipid concentrations there is a temperature and salt effect on the observed interaction, which is related to a conformational change of the peptide. Signal sequences show clearly conformational flexibility in responds to environmental conditions. Under the conditions used in this study FTIR spectra of PhoE signal peptide-DOPG monolayers show a high content of β-structure and β-turn.