title: Electrostatic contributions to indole-lipid interactions.
abstract: The role of electrostatic forces in indole-lipid interactions was studied by (1)H and (2)H NMR in ether- and ester-linked phospholipid bilayers with incorporated indole. Indole-ring-current-induced (1)H NMR chemical shifts of lipid resonances in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine, and 1,2-di-O-octadecenyl-sn-glycero-3-phosphomethanol show a bimodal indole distribution, with indole residing at the upper hydrocarbon chain/glycerol region of the lipid and near the choline group, when present. (2)H NMR of indole-d(7)-incorporated lipid bilayers reveals that the former site is occupied by about two-thirds of the indole, which adopts a distinct preferred orientation with respect to the bilayer normal. The results suggest that the upper hydrocarbon chain/glycerol location is dictated by many factors, including interactions with the electric charges and dipoles, van der Waals interactions, entropic contributions, and hydrogen bonding. Indole diffusion rates are higher in lipids with ester bonds and lower in choline-containing lipids, suggesting that interactions between indole and carbonyl groups are of minor importance for lipid-indole association and that cation-pi interactions with choline drive the second indole location. Nuclear Overhauser effect spectroscopy cross-relaxation rates suggest a 30-ns lifetime for indole-lipid associations. These results may have important implications for sidedness and structural transitions in tryptophan-rich membrane proteins.
authors.affiliation: Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 5625 Fishers Lane, Room 3N07, Bethesda, Maryland 20892-9410, USA.
authors.forename: Holly C
authors.initials: HC
authors.lastname: Gaede
authors.forename: Wai-Ming
authors.initials: WM
authors.lastname: Yau
authors.forename: Klaus
authors.initials: K
authors.lastname: Gawrisch
mesh_terms: D002794:Choline / Q000737:chemistry; D003903:Deuterium / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010743:Phospholipids / Q000737:chemistry*; D011522:Protons; D055672:Static Electricity; D014364:Tryptophan / Q000737:chemistry
chemical_list: D007211:Indoles; D008051:Lipid Bilayers; D010743:Phospholipids; D011522:Protons; C030374:indole; D014364:Tryptophan; D003903:Deuterium; D002794:Choline