Solid‐state NMR investigations of interaction contributions that determine the alignment of helical polypeptides in biological membranes

Abstract

Helical peptides reconstituted into oriented phospholipid bilayers were studied by proton-decoupled 15 N solid-state NMR spectroscopy. Whereas hydrophobic channel peptides, such as the N-terminal region of Vpu of HIV-1, adopt transmembrane orientations, amphipathic peptide antibiotics are oriented parallel to the bilayer surface. The interaction contributions that determine the alignment of helical peptides in lipid membranes were analysed using model sequences, and peptides that change their topology in a pH-dependent manner have been designed. The energy contributions of histidines, lysines, leucines and alanines as well as the alignment of peptides and phospholipids under conditions of hydrophobic mismatch have been investigated in considerable detail. ß 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.Key words: Oriented bilayer ; Transmembrane polypeptide; Amphipathic peptide; Membrane equilibrium; Hydrophobicity scale; Interface Although membrane proteins constitute about one third of the expressed reading frames, only a few high-resolution structures of this important class of proteins have become available [1,2]. This lack of conformational information is due to the di¤culties encountered during the expression and puri¢cation of hydrophobic proteins and their resistance to crystallization, which would be necessary for X-ray or electron di¡raction. The organization of integral membrane proteins is characterized by the separation of hydrophobic membrane-spanning and hydrophilic membrane-£anking regions (reviewed in [13 ]) with two major motifs, i.e. helical domains and, for proteins of the bacterial outer membranes, L-barrel structures being observed [1].At the same time DNA sequence analysis is fast and routine; therefore, structure prediction algorithms identifying membrane-spanning domains remain an important source of information. These protocols involve a ¢rst step in which the primary sequence is searched for hydrophobic, putatively transmembrane helical domains [4^6]. Clearly the accuracy of these predictions is strongly dependent on the quality of the underlying data base which assigns hydrophobicity values to individual amino acids.An accurate knowledge of the interaction contributions that determine the alignment of membrane-associated helices is of great importance not only for the prediction of membrane protein structure, but also for our understanding of the functional mechanisms of smaller single helical domain polypeptides. Hydrophobic or amphipathic helical peptides exhibit a multitude of functional properties, including antibiotic, fusogenic and channel activities [7,8]. However, due to the multitude of conformations and the dynamic properties of these sequences in the presence of lipid bilayers, it is often di¤cult to directly correlate structural data with functional aspects [9,10]. For example, it has been suggested that the membrane-permeabilizing properties of magainin/PGS-type antibiotic peptides are caused by transmem...

Histidine-rich amphipathic peptide antibiotics promote efficient delivery of DNA into mammalian cells

“…Experiments with this latter technique also indicated that the in-plane-transmembrane transition is reversible (19). Interestingly, in this study all peptides exhibiting high transfection efficiencies also show pH-dependent membrane alignments with transition midpoints around pH 6 (16,17). This suggests that pH-dependent membrane insertion of the peptides constitutes an important part of the DNA import mechanism.…”

The Crystal Structure of the Periplasmic Domain of the Escherichia coli Membrane Protein Insertase YidC Contains a Substrate Binding Cleft

“…6C) that could attach or even insert into the membrane (70,71). This region is conserved in YidC homologs that do not have a P1D, suggesting an important and conserved role of this region for the function of YidC (see above).…”

How Hydrophobic Is Alanine?

“…Thermodynamic analysis of the binding of pentaeptides to model lipid bilayers and the partition of tripeptides between water and octanol also indicates that Ala has a slight preference for the lipid-water interface region over the acyl chain region (17). Solid-state NMR studies of peptide-bilayer interactions point in the same direction (33). It thus appears that the interactions between a nascent polypeptide chain and the ER translocon that determine membrane protein topology in vivo are remarkably similar to peptide-lipid interactions in highly simplified in vitro systems.…”