Bolalipid membrane structure revealed by solid-state 2H NMR spectroscopy

Abstract

Membranes made from three specifically deuterium-labeled ether-linked bolalipids, [1',1',20',20'-2H4]C20BAS-PC, [2',2',19',19'-2H4]C20BAS-PC, or [10',11'-2H2]C20BAS-PC, were analyzed by 2H NMR spectroscopy. Unlike more common monopolar, ester-linked phospholipids, C20BAS-PC exhibits a high degree of orientational order throughout the membrane and the sn-1 chain of the lipid initially penetrates the bilayer at an orientation different from that of the bilayer normal, resulting in inequivalent deuterium atoms at the C1 position. The approximate hydrophobic layer thickness and area per lipid are 18.4 A and 60.4 A2, respectively, at 25 degrees C, and their respective thermal expansion coefficients are within 20% of the monopolar phospholipid, DLPC.

Figure 1

(A) Structure of non-deuterated C₂₀BAS-PC. (B) Powder-type (red) and de-Paked (blue) ²H NMR spectra of [1′,1′,20′,20′-²H₄]C₂₀BAS-PC (1), [2′,2′,19′,19′-²H₄]C₂₀BAS-PC (2), and [10′,11′-²H₂]C₂₀BAS-PC (3) at 25 °C. (C) Powder-type ²H NMR spectra of [10′,11′-²H₂]C₂₀BAS-PC at −60, 10, 15, 35, and 55 °C.

Figure 2

(A) De-Paked quadrupolar splittings (Δν_Q) of [10′,11′-²H₂]C₂₀-BAS-PC as a function of temperature. (B) Order parameters $\mid S_{\text{CD}}^{(i)}\mid$ of C₂₀-BAS-PC (blue) at 25 °C and DLPC (red) at 30 °C as a function of carbon number.

Figure 3

(A) Hydrophobic layer thickness (D_C) for [2′,2′,19′,19′-²H₄]C₂₀-BAS-PC (green) and DLPC (red) as a function of temperature. (B) Natural logarithm of hydrophobic layer thickness, (C) area per lipid, and (D) natural logarithm of area per lipid as a function of temperature.