Transmembrane Polarity Profiles

Transcription

1 Transmembrane Polarity Profiles fluid membranes normalised profile, Δc(x) C1 C3 C5 polarity /H O C7 C9 C11 C13 NO C13 C11 C9 C7 C5 C3 C O membrane position, x (nm) P HO =6.1-3 cm/s P O =1 cm/s P NO =16 cm/s hyperfine coupling a o N relaxation enhancement Δ(1/T 1e )

2 CW-EPR: Polarity dependence of isotropic hyperfine coupling aprotic media: a N o = a ε = 1 o + K Block-Walker reaction field: f BW protic media: v f ( ε r ) n 1 1+ f ( ε ) r n + 3ε r ln ε r 6 ( ε r ) = ε ln ε ε + 1 ln ε r r r Marsh (8) J. Magn. Reson. 19, 6-67 a N o = ( 1 f ) = a N, + h a N, N N ( a a ) K [ OH], h + f h, a N, h A, h r a N o (mt) a N o (mt) Onsager Block-Walker r/r eff TOAC: ε/ε B f BW (ε)/(1-f BW (ε)/4) da N o /d[oh]=.x1-3 mt/m TOAC: K v =8.9x1 - mt DOXYL: K v =8.7x1 - mt DOXYL: da N o /d[oh]=.3x1-3 mt/m [OH] (M)

3 1..8 Correlation of lipid-chain O -profile with linewidth: ΔΔH L =ΔT 1e /γ e lipid chain α-helix Cys-SDSL lipids: Δz =.1 nm/ch (Dzikovski et al., 3) O -induced relaxation enhancement, Δ(1/T 1e ) saturation: γ e HT T 1 e 1e lipid chain α-helix distance from mid-plane, z-d (nm) z o =.5 nm, λ =. nm α-helix: Δz =.15 nm/aa (Nielsen et al., 5) GW (LA) m C(LA) n LW A S S Profile: Δ ( 1/ T ) = ( R R ) 1e Marsh et al., 6 1 O N O z d N O 1 1+ exp(( z zo + d) / λ) 1 + R 1 exp(( z zo d) / ) + + λ

4 3-pulse H-ESEEM spectroscopy - measures D O penetration directly

5 Standardised ESEEM Intensities Fourier transform V(τ,T) <V(τ,T)> π/-τ-π/-t-π/-τ-echo I ( ω ) k ΔT = N j= V norm ( τ, T + jδt ) exp ( iω (τ + T + jδt )) o ω = πk /( NΔT ), k = N / N / k + k o 4 14 absolute value spectrum: V(τ,T)/<V(τ,T)> normalised ESEEM, V norm (τ,t) ΔT = 1 ns normalised intensity, I(ω) (ns) H 1 H pulse spacing, T (μs) frequency, ω/π (MHz)

6 Water-penetration profile measured by ESEEM spectroscopy a N o (mt) DPPC DPPC+chol DPPC+chol D O-amplitude, I(ω D ) (ns) HEADGROUP DPPC TERMINAL CH chain position, n chain position, n (C-atom)

7 D O ESEEM simulation from DFT calculations "free" in membrane classical dipolar H-bonded I broad quantum chemical (DFT) DFT calibration: I broad = 115 ns/d O

8 Hydrogen bonding equilibria K NO+ HO NO (H O) K/ NO HO + HO NO (H O) K = "single site" K A I f broad I o 1HO K[H O] = 1+ K[H O] = 1/ K[H O] Ibroad = f1h O Io f HO K[H O] I free I broad

9 High-Field EPR - polarity dependence of g-tensor (Kawamura et al., 1967) N O:---H g xx = g e + O E ( ( n) C ) p O, y E ζ ρ n O ( n) C O, y = coefft. of p y in O lone-pair orbital - depends on H-bonding

10 g xx transmembrane polarity profile 7. δδg Δg xx xx = ρ ρ N π o π δa A zz zz δc δδenπ * ny + ΔEnπ * cny (g xx -g e )x HEADGROUP δg xx =-6x1-4 TERMINAL CH n-pcsl: n = H-bond chain position, n decreasing polarity increases g xx (g xx -g e )x terminal CH 3 g xx / A zz = -.4 T A zz (mt) 7 65 headgroup 4

11 Water H-bonding: comparison with density functional calculations Owenius, R., Engström, M., Lindgren, M. and Huber, M., 1. g xx -values: DFT: H-bonding: Exptl. (C14-C5): Δ g xx Δg xx = = 8. 1 = HO molecules 1 HO HO (4% chol) (at C5,C6 position) g xx vs. A zz gradients: DFT: H-bonding: Exptl. (C4-C14): g A g A xx zz xx zz 1 =.3 T ( H - bond, HO) =.4 ±.1 T 1 (4% chol)

12 Polarity/H O Inhomogeneity (g-strain) 36 GHz DMPC + 5-PC. mt 94 GHz DMPC/Chol (4 mol%).88 mt 5-PC Field (Tesla) 8-PC Inhomogeneous broadening: δδh (5 9) = ±.4 mt δδ ~ ± 1 g xx ±.5 H 4 O (94 GHz).47 mt 9-PC Field (Tesla)

13 Polarity profile at lipid-protein interface Transmembrane 16-kDa proteolipid subunit c of the vacuolar H + -ATPase A zz (gauss) 16-kDa DMPC/chol n (C-atom) subunit c - broadening of profile - higher polarity at lipid-protein interface in membrane interior

14 TOAC-labelled alamethicin in membranes 1 8 Ac-Aib-Pro-Aib-Ala-Aib-Ala-Glu(OMe)-Aib-Val-Aib-Gly- 16 Leu-Aib-Pro-Val-Aib-Aib-Glu(OMe)-Glu(OMe)-Phol O N TOAC 8 C NH C'O TOAC Me Me C NH C'O Aib helicogenic

15 Isotropic 14 N-hyperfine coupling TOAC-alamethicin/diC(14:) phosphatidylcholine TOAC 8 1 C a eff o eff eff ( A + A ) 1 = // 3 C 3 C 5 C 8 C a eff (mt) o TOAC A A eff // eff = = A A max min A min A max + 1.3G G log 1 1 A A max zz A A min xx temperature ( o C) TOAC 8 - fast motional limit achieved at ca. 5 C for TOAC 8, and > 6 C for TOAC 16

16 Positioning of TOAC n -alamethicin in membrane dic(n:)ptdcho a on calibration membrane thickness (X-ray). dic14pc TOAC 1 Δa o (gauss) dic14pc TOAC 1 dic16pc dic14pc TOAC 16 dic16pc TOAC 8 bilayer thickness, d (nm) 1-1 TOAC 8 TOAC 16 Fol d C d B -.6 dic16pc position, C-n chainlength, N (C-atom) - position relative to mid-plane remains fixed

17 D O-ESEEM TOAC-alamethicin/diC(18:1)PtdCho standardised intensity, I(ω) (ns) H H H frequency, ω/π (MHz) TOAC 1 TOAC 8 TOAC 16 D O-amplitude, I(ω D ) (ns) TOAC position, C-n TOAC 1 TOAC 8 TOAC 1 : headgroup region TOAC 8, TOAC 16 : C-1 positions on opposite sides of membrane

18 -SH Groups on Na,K-ATPase Class I cytoplasmic standardised intensity, I(ω) (ns) Class II intramembrane frequency, ω/π (MHz)

19 Fatty Acid Binding Site/Human Serum Albumin 15 H HSA/5-SASL 1 5 Standardised intensity, I(ω) (ns) 15 H H H H HSA/7-SASL HSA/1-SASL HSA/1-SASL HSA/16-SASL D O-Amplitude (ns) surface binding pocket lipid bilayer frequency, ω/π (MHz) Spin-label position, C-n

20 Conclusions 1) Hyperfine interactions depend on polarity (Block-Walker reaction field) and H-bonding. ) D O-ESEEM resolves H-bonded and "free" intramembrane water. 3) HF-EPR distinguishes protic from aprotic environments (g xx vs. A zz ), and directly detects heterogeneity in H-bonded waters. 4) Sigmoidal polarity profile of lipid bilayers is smeared out at the lipid-protein interface. 5) Alamethicin monomers are symmetrically disposed w.r.t. the bilayer midplane in membranes of different thicknesses.

21 Collaborators ESEEM Rosa Bartucci Rita Guzzi Francesco de Simone Luigi Sportelli (University of Calabria) High-Field EPR Dieter Kurad Gunnar Jeschke (MPI Polymer Res., Mainz) T 1 -Enhancements (O, NO) Vsevolod A. Livshits Boris Dzikovski (Centre of Photochemistry, Moscow) Tibor Páli Saviana Nedeianu (Biological Research Centre, Szeged) TOAC-Alamethicin Claudio Toniolo Micha Jost Cristina Peggion Marta De Zotti (University of Padua) Vacuolar ATPase (16-kDa) Malcolm Finbow (University of Glasgow) Na,K-ATPase Mikael Esmann (University of Aarhus)