Membrane incorporation and induction of secondary structure of synthetic peptides corresponding to the N-terminal signal sequences of the glucitol and mannitol permeases of Escherichia coli.
The 22-residue synthetic signal peptide of the glucitol permease (Enzyme IIgut of the bacterial phosphotransferase system; gut22), which in the intact protein is believed to function in envelope targeting, was found to insert into phospholipid monolayers of various phospholipid compositions up to high limiting pressures (36-41 milliNewton/m). The partition coefficient, derived from monolayer area expansion experiments, was greatest for the negatively charged gut22 when partitioning into monolayers of the zwitterionic lipid 1-palmitoyl-2-oleoyl-3-sn-phosphatidylcholine (about 1.1 X 10(5] as compared with that obtained with a mixture of 1-palmitoyl-2-oleoyl-3-sn-phosphatidylcholine and the negatively charged lipids 1-palmitoyl-2-oleoyl-3-sn-phosphatidylglycerol and cardiolipin. Gut22 contains a titratable histidyl residue (pKa = 6.8), and its protonation decreased the relative monolayer area increase 3-fold. Circular dichroism spectra showed that gut22 formed an amphiphilic alpha-helix when incorporated into lipid membranes (estimated percent helix = 65%). Fluorescence measurements indicated that tryptophan 11 is in a more hydrophobic environment in the presence of lipid than in its absence, with the environment being more hydrophobic at pH 5 than at pH 8. The more hydrophilic 15-residue signal peptide of the mannitol permease (mtl15) also incorporated into monolayers and detergent micelles (although to a lesser extent) with induction of secondary structure. Based on these results and a parallel with mitochondrial targeting in eucaryotes, we suggest that the induction of N-terminal amphiphilic structures and their association with a hydrophobic-hydrophilic interface are important for envelope targeting and the initiation of the membrane insertion of bacterial phosphoenol-pyruvate-dependent phosphotransferase system permeases.
Tamm
L K
LK
Biocenter, University of Basel, Switzerland.
Tomich
J M
JM
Saier
M H
MH
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology; D002942:Circular Dichroism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000096:biosynthesis*; D011312:Pressure; D011487:Protein Conformation; D021382:Protein Sorting Signals / Q000138:chemical synthesis / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013499:Surface Properties
D029968:Escherichia coli Proteins; D009004:Monosaccharide Transport Proteins; D021382:Protein Sorting Signals; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C022358:mannitol PTS permease, E coli; C058558:phosphoenolpyruvate glucitol phosphotransferase