Effects of Aromatic Residues at the Ends of Transmembrane α-Helices on Helix Interactions with Lipid Bilayers

Abstract

We have studied the effects of aromatic residues at the ends of peptides of the type Ac-KKGL(n)()WL(m)()KKA-amide on their interactions with lipid bilayers as a function of lipid fatty acyl chain length, physical phase, and charge. Peptide Ac-KKGFL(6)WL(8)FKKA-amide (F(2)L(14)) incorporated into bilayers of phosphatidylcholines containing monounsaturated fatty acyl chains of lengths C14-C24 at a peptide:lipid molar ratio of 1:100 in contrast to Ac-KKGL(7)WL(9)KKA-amide (L(16)) which did not incorporate at all into dierucoylphosphatidylcholine [di(C24:1)PC]; Ac-KKGYL(6)WL(8)YKKA-amide (Y(2)L(14)) incorporated partly into di(C24:1)PC. Lipid-binding constants relative to that for dioleoylphosphatidylcholine (C18:1)PC were obtained using a fluorescence quenching method. For Y(2)L(14) and F(2)L(14), relative lipid-binding constants increased with increasing fatty acyl chain length from C14 to C24; strongest binding did not occur at the point where the hydrophobic length of the peptide equalled the hydrophobic thickness of the bilayer. For Ac-KKGYL(9)WL(11)YKKA-amide (Y(2)L(20)), increasing chain length from C18 to C24 had little effect on relative binding constants. Anionic phospholipids bound more strongly than zwitterionic phospholipids to Y(2)L(14) and Y(2)L(20) but effects of charge were relatively small. In two phase (gel and liquid crystalline) mixtures, all the peptides partitioned more strongly into liquid crystalline than gel phase; effects were independent of the structure of the peptide or of the lipid (dipalmitoylphosphatidylcholine or bovine brain sphingomyelin). Addition of cholesterol had little effect on incorporation of the peptides into lipid bilayers. It is concluded that the presence of aromatic residues at the ends of transmembrane alpha-helices effectively buffers them against changes in bilayer thickness caused either by an increase in the chain length of the phospholipid or by the presence of cholesterol.

Channel Replacement Therapy for Cystic Fibrosis

“…In addition to stabilizing the concentration of monomer in aqueous solutions, inclusion of any C-terminal aromatic residue provided a lipid/water interfacial anchor. As was seen with W, F residues are commonly present (and Y to a lesser extent) at the hydrophobic/hydrophilic interface for TM segments of membrane proteins (Braun and von Heijne, 1999;Mall et al, 2000;Demmers et al, 2001;de Planque et al, 2003;Granseth et al, 2005;van der Wel et al, 2007;Hong et al, 2007 Comparing all of the summarized data in Tables 3 and 4 and the profiles shown in Figs. 16 and 17, the sequences displaying the highest ion transport activity and the second and third most left-shifted k 1/2 values are both W containing peptide sequences, NK 4 -M2GlyR-p22 T19R, S22W and NK 4 -M2GlyR-p22 Q21W, S22R.…”

“…A propensity for tryptophans residing at the aqueous/lipid interface also had been observed and tested by others (Braun and von Heijne, 1999;Mall et al, 2000;Demmers et al, 2001;de Planque et al, 2003;Granseth et al, 2005;van der Wel et al, 2007;Hong et al, 2007). Placing a W at the Cterminus sets the registry of the TM segment that spans the bilayer.…”

Domain Formation in Phosphatidylcholine Bilayers Containing Transmembrane Peptides: Specific Effects of Flanking Residues

“…Following the positive inside rule, they are preferentially located on the cis-side of membranes, (12), where they associate with anionic phospholipids (13), fulfilling a topology-determining role (14). When flanking a hydrophobic R-helix in transmembrane model peptides, lysines showed a distinct preference for the hydrophilic side of the interfacial region, close to the phosphate groups of the surrounding lipid bilayer (5).To gain more insight in these interfacial interactions, model peptides have been used (5,15,16). An example of synthetic model peptides are the so-called WALP 1 peptides (17).…”

“…To gain more insight in these interfacial interactions, model peptides have been used (5,15,16). An example of synthetic model peptides are the so-called WALP 1 peptides (17).…”

Tryptophan Scanning Reveals Dense Packing of Connexin Transmembrane Domains in Gap Junction Channels Composed of Connexin32

“…(8) and also within the membrane-spanning regions of the Cx26 atomic model (10). Tryptophan substitutions were avoided at predicted membrane boundaries as large aromatic side chains can influence positioning of helices within the membrane (32). In the Cx26 crystal structure, helices TM2 and TM3 extend beyond the membrane at the cytosolic face (10), and these cytoplasmic regions were not analyzed in this study.…”