Structure and dynamics of the gammaM4 transmembrane domain of the acetylcholine receptor in lipid bilayers: insights into receptor assembly and function

Mol Membr Biol. 2006 Jul-Aug;23(4):305-15. doi: 10.1080/09687860600703613.

Abstract

A 28-mer peptide (gammaM4) corresponding to the fourth transmembrane segment of the nicotinic acetylcholine receptor (AChR) gamma-subunit, with a single tryptophan residue (Trp6), was reconstituted into lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), loaded with either high or low amounts of cholesterol, i.e., in the conjugated liquid-ordered and liquid-disordered phases, respectively, at room temperature. By making use of the Trp intrinsic fluorescence, both steady-state and time-resolved fluorescence techniques were employed, namely, red-edge excitation shift effect, decay-associated spectra (DAS), and time-resolved anisotropy. The results obtained here, together with previous studies on the same reconstituted peptide, indicate that: (i) Trp6 is strongly anchored in the bilayer with a defined transverse location; (ii) the modifications in the measured DAS are related to the complex result of a self-quenching process on the decay parameters; (iii) the wobbling movement of the indole moiety of Trp6 is fast but severely restricted in amplitude; and, (iv) in the liquid-ordered phase, the bilayer properties and the tilt angle of the peptide enhance peptide-peptide interactions, with the formation of peptide rich patches and possibly some anti-parallel helix-helix aggregates, showing different dynamics from that of the peptide in the liquid-disordered phase where the peptide is randomly distributed.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Fluorescence Polarization
  • Humans
  • Lipid Bilayers / chemistry*
  • Peptides / chemistry
  • Phosphatidylcholines / chemistry*
  • Protein Conformation
  • Protein Structure, Tertiary
  • Receptors, Nicotinic / chemistry*
  • Tryptophan / chemistry*

Substances

  • Lipid Bilayers
  • Peptides
  • Phosphatidylcholines
  • Receptors, Nicotinic
  • Tryptophan
  • 1-palmitoyl-2-oleoylphosphatidylcholine