ESEEM Measurements of Local Water Concentration in D2O-Containing Spin-Labeled Systems

SARS-CoV fusion peptides induce membrane surface ordering and curvature

“…7A), which arises from the quadrupole interaction between the electron spin and non-2 H-bonded water molecules inside the bilayer 54 . Both Δ and I( 2 H) have been found to depend linearly and nonlinearly, respectively, on the concentration of free water molecules at a distance of 0.5 to 1.0 nm 56 .…”

“…Since the ordering effect of the lipid head group has been attributed to bilayer dehydration 53 , we used ESEEM spectroscopy to find out whether the peptide-induced ordering of anionic vesicles is possibly related to membrane dehydration, as suggested as a general fusion mechanism of other class I fusion peptides 46,47 . ESEEM has been successfully applied to examine the penetration depth profile of deuterium-substituted molecules, such as water, glycerol, and sugar inside lipid bilayers [54][55][56][57] as well as to investigate the water permeation at protein/peptide-lipid interface of membrane-interacting peptides and membrane proteins [58][59][60] . Here we used a D 2 O-containing buffer to probe the deuterium environment surrounding the spin labels DOPTC, 5-PCSL, and 16-PCSL ( Supplementary Fig.…”

“…The different spin labels allowed investigating the changes promoted by the peptides in the water content from the lipid/water interface down to the hydrophobic core of the bilayers. Changes in the modulation depth of the time-domain ESEEM spectra or in the deuterium spectral density yields information about D 2 O molecules situated near the nitroxide within a distance range of up to 1.0 nm, which is the known spatial reach of the method 56 . Figure 7A shows the spectral density of the spin-labeled lipids in the peptide-free and peptide-containing lipid vesicles (the normalized time-domain stimulated echo signals are given in the Supplementary Fig.…”

“…This finding implies that both peptides interact with POPC/POPG membranes and displace free water molecules from their hydrophobic core. Theoretical calculations from Milov et al indicated that nitroxide-deuterons interactions spread to around 1 nm 56 . Therefore, the spin label at C 5 position is able to monitor water density around C 5 up to the level of the carbonyl-glycerol and phosphocholine regions (distant about 1.0 nm from C 5 ) 61,63 .…”

“…Therefore, the spin label at C 5 position is able to monitor water density around C 5 up to the level of the carbonyl-glycerol and phosphocholine regions (distant about 1.0 nm from C 5 ) 61,63 . Thus, the contribution from bulk water molecules to the spectral density of 5-PCSL is negligible 54,56 . The significant 27% decrease of Δ for 5-PCSL in the peptide-containing membranes, relative to the peptide-free vesicles ( Supplementary Table S7, Fig.…”