title: Structure and dynamics of the gammaM4 transmembrane domain of the acetylcholine receptor in lipid bilayers: insights into receptor assembly and function.
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.
authors.affiliation: Centro de Química e Bioquímica, Faculdade de Ciências de Lisboa, Campo Grande, Lisboa, Portugal. r.almeida@mail.ist.utl.pt
authors.forename: Rodrigo F M
authors.initials: RF
authors.lastname: De Almeida
authors.forename: Luís M S
authors.initials: LM
authors.lastname: Loura
authors.forename: Manuel
authors.initials: M
authors.lastname: Prieto
authors.forename: Anthony
authors.initials: A
authors.lastname: Watts
authors.forename: Aleksandre
authors.initials: A
authors.lastname: Fedorov
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Barrantes
mesh_terms: D000818:Animals; D005454:Fluorescence Polarization; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D010713:Phosphatidylcholines; D011978:Receptors, Nicotinic; D014364:Tryptophan; C028694:1-palmitoyl-2-oleoylphosphatidylcholine