Interfacial anchor properties of tryptophan residues in transmembrane peptides can dominate over hydrophobic matching effects in peptide-lipid interactions.
Membrane model systems consisting of phosphatidylcholines and hydrophobic alpha-helical peptides with tryptophan flanking residues, a characteristic motif for transmembrane protein segments, were used to investigate the contribution of tryptophans to peptide-lipid interactions. Peptides of different lengths and with the flanking tryptophans at different positions in the sequence were incorporated in relatively thick or thin lipid bilayers. The organization of the systems was assessed by NMR methods and by hydrogen/deuterium exchange in combination with mass spectrometry. Previously, it was found that relatively short peptides induce nonlamellar phases and that relatively long analogues order the lipid acyl chains in response to peptide-bilayer mismatch. Here it is shown that these effects do not correlate with the total hydrophobic peptide length, but instead with the length of the stretch between the flanking tryptophan residues. The tryptophan indole ring was consistently found to be positioned near the lipid carbonyl moieties, regardless of the peptide-lipid combination, as indicated by magic angle spinning NMR measurements. These observations suggest that the lipid adaptations are not primarily directed to avoid a peptide-lipid hydrophobic mismatch, but instead to prevent displacement of the tryptophan side chains from the polar-apolar interface. In contrast, long lysine-flanked analogues fully associate with a bilayer without significant lipid adaptations, and hydrogen/deuterium exchange experiments indicate that this is achieved by simply exposing more (hydrophobic) residues to the lipid headgroup region. The results highlight the specific properties that are imposed on transmembrane protein segments by flanking tryptophan residues.
de Planque
Maurits R R
MR
Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. m.r.r.deplanque@chem.uu.nl
Bonev
Boyan B
BB
Demmers
Jeroen A A
JA
Greathouse
Denise V
DV
Koeppe
Roger E
RE
Separovic
Frances
F
Watts
Anthony
A
Killian
J Antoinette
JA
D000409:Alanine / Q000737:chemistry; D002942:Circular Dichroism; D007930:Leucine / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins / Q000737:chemistry*; D008956:Models, Chemical; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000737:chemistry; D017433:Protein Structure, Secondary; D014364:Tryptophan / Q000737:chemistry*
D008051:Lipid Bilayers; D008565:Membrane Proteins; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D014364:Tryptophan; D007930:Leucine; D008239:Lysine; D000409:Alanine