Different Membrane Anchoring Positions of Tryptophan and Lysine in Synthetic Transmembrane α-Helical Peptides

Abstract

Specific interactions of membrane proteins with the membrane interfacial region potentially define protein position with respect to the lipid environment. We investigated the proposed roles of tryptophan and lysine side chains as "anchoring" residues of transmembrane proteins. Model systems were employed, consisting of phosphatidylcholine lipids and hydrophobic ␣-helical peptides, flanked either by tryptophans or lysines. Peptides were incorporated in bilayers of different thickness, and effects on lipid structure were analyzed. Induction of nonbilayer phases and also increases in bilayer thickness were observed that could be explained by a tendency of Trp as well as Lys residues to maintain interactions with the interfacial region. However, effects of the two peptides were remarkably different, indicating affinities of Trp and Lys for different sites at the interface. Our data support a model in which the Trp side chain has a specific affinity for a well defined site near the lipid carbonyl region, while the lysine side chain prefers to be located closer to the aqueous phase, near the lipid phosphate group. The information obtained in this study may further our understanding of the architecture of transmembrane proteins and may prove useful for refining prediction methods for transmembrane segments.In biological membranes, a variety of interactions can occur between lipids and proteins that affect protein as well as lipid properties and in which both the hydrophobic membrane core and the more polar membrane interfaces can be involved (1-3). Membrane proteins are able to span the lipid bilayer through interactions of their exposed hydrophobic segments with the lipid hydrocarbon acyl chains. In general, the length of these hydrophobic segments will approximately match the membrane hydrophobic thickness. However, also a mismatch between protein hydrophobic length and membrane hydrophobic thickness may occur. Such a mismatch can have considerable influence on membrane structure and function (reviewed in Ref. 4) and may, for example, be involved in protein sorting, microdomain formation, changes in protein activity, or changes in lipid structure and organization.In contrast to the hydrophobic core of a membrane, the membrane interface presents a complex and heterogeneous chemical environment, which accounts for a relatively large proportion of the total bilayer thickness (3). Specific interactions of membrane proteins with the interfacial region of the lipids may influence many functional processes, such as for instance membrane protein assembly, topology of membrane proteins, the mode of protein insertion into the membrane, and protein anchoring to the membrane. In addition, such interactions may play a determining role in hydrophobic mismatch (4).Analyses of the structure of transmembrane proteins suggest that two types of amino acids may be of special importance for interactions of membrane proteins with the interfacial region: aromatic amino acids, in particular tryptophans, which are enriched at both ends of tr...

Conformation of the synaptobrevin transmembrane domain

“…5). Strong interactions between tryptophan and the interfacial region of the membrane can change bilayer thickness or exclude the peptide from the membrane to satisfy the partitioning requirements (59)(60)(61)(62). If synaptobrevin were incorporated with a more perpendicular tilt angle, tryptophan partitioning would cause the lysine residues to be completely buried, which is energetically less favorable (63).…”

Solid-State17O NMR as a Probe for Structural Studies of Proteins in Biomembranes

“…WALP23 is a synthetic peptide which represents a consensus sequence for transmembrane protein segments. 14 This hydrophobic peptide forms well-defined and wellcharacterized transmembrane R-helices 14 and has special relevance for the packing of R-helices in polytopic proteins, such as G-proteincoupled receptors.…”

“…WALP23 was synthesized and transmembranously incorporated into multilamellar vesicles (MLVs) of 1,2-distearoyl-sn-glycerol-3-phosphatidylcholine (DSPC) lipids. 14 The 17 O NMR experiments were carried out on Chemagnetics Infinity 600 and Varian/Magnex 800 wide-bore 89 mm spectrometers at frequencies of 81.345 and 108.419 MHz for 17 O, respectively. MAS was performed at a spin rate of 11-22 kHz.…”

A Synergistic Effect between Cholesterol and Tryptophan-Flanked Transmembrane Helices Modulates Membrane Curvature

“…1,2-dieicosenoyl-sn-glycero-3-phosphocholine (di-20:1 c -PC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (di-18:1 c -PC), 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (di-16:1 c -PC), 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (di-14:1 c -PC), 1-oleoyl-sn-glycero-3-phosphocholine (lysoPC), and cholesterol were purchased from Avanti Polar Lipids (Alabaster, AL). Peptides were synthesized, purified, and analyzed by analytical high-performance liquid chromatography and electrospray mass spectrometry as described before (12). The amino acid sequences of the peptides used were Ac-GWW(LA) 8 LWWA-amide (WALP23), Ac-GWW-(LA) 10 LWWA-Etn (WALP27), Ac-GKK(LA) 8 LKKA-amide (KALP23), and GHH(LA) 8 LHHA-amide (HALP23).…”

“…In contrast to the 31 P NMR spectrum of the di-18:1 c -PC/cholesterol/WALP23 50:25:1 mixture ( Figure 4A), no isotropic signal is present in the spectrum when KALP23 is incorporated instead of WALP23 ( Figure 4C). This is unlikely to be due to a difference in the effective hydrophobic length of these peptides (12), because no isotropic signal is observed when the mismatch is varied by incorporating KALP23 in mixtures containing cholesterol and either di-16:1 c -PC or di-20:1 c -PC (data not shown).…”