Low-Temperature Dynamics of Chain-Labeled Lipids in Ester- and Ether-Linked Phosphatidylcholine Membranes

Abstract

Continuous wave electron paramagnetic resonance spectroscopy and two-pulse echo detected spectra of chain-labeled lipids are used to study the dynamics of frozen lipid membranes over the temperature range 77-260 K. Bilayers of ester-linked dihexadecanoylphosphatidylcholine (DPPC) with noninterdigitated chains and ether-linked dihexadecyl phosphatidylcholine (DHPC) with interdigitated chains are considered. Rapid stochastic librations of small angular amplitude are found in both lipid matrices. In noninterdigitated DPPC bilayers, the mean-square angular amplitude, [Formula: see text], of the motion increases with temperature and it is larger close to the chain termini than close to the polar/apolar interface. In contrast, in interdigitated DHPC lamellae, [Formula: see text] is small and temperature and label-position independent at low temperature and increases steeply at high temperature. The rotational correlation time, τ, of librations lies in the subnanosecond range for DPPC and in the nanosecond range for DHPC. In all membrane samples, the temperature dependence of [Formula: see text] resembles that of the mean-square atomic displacement revealed by neutron scattering and a dynamical transition is detected in the range 210-240 K. The results highlight the librational oscillations and the glass-like behavior in bilayer and interdigitated lipid membranes.

Evidence for an Ordering Transition near 120 K in an Intrinsically Disordered Protein, Casein

“…Regarding the CW EPR data, for the spin-labeled DPPC bilayer the value was found to start to increase above 200 K [ 19 ], which is also in agreement with data in Figure 4 for lysozyme. For spin-labeled DOPC bilayer, when the spin label is located near the bilayer surface, the value starts to increase at 240 K [ 28 ].…”

“…To further support the suggested explanation of the kink for the Δ W temperature dependence for casein near 120 K as evidence for the disorder–order transition, we turn to comparison with the analogous ESE studies of stochastic molecular librations in spin-labeled gel-phase phospholipid bilayers composed either of conformationally ordered or conformationally disordered lipids. These studies were performed for the bilayers composed of saturated 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) lipids [ 16 , 19 , 28 ], mono-unsaturated 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphocholine (POPC) lipids [ 16 , 28 ] doubly-unsaturated 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) lipids [ 17 , 28 ]. In these systems, DPPC presents an example of conformationally ordered molecule while POPC and DOPC are conformationally disordered.…”

“…Using this approach, molecular packing was studied in gel-phase biological membranes (lipid bilayers) [ 16 , 17 , 18 , 19 ] and in glassy ionic liquids [ 20 , 21 , 22 , 23 ]. Further, interaction of free fatty acids with proteins [ 24 ] and interaction of sugars with biological membranes [ 25 ] was investigated.…”

“…Further, interaction of free fatty acids with proteins [ 24 ] and interaction of sugars with biological membranes [ 25 ] was investigated. Stochastic molecular librations are sensitive to a so-called dynamical transition in proteins and in other biological systems [ 16 , 19 , 26 , 27 , 28 ], which is known occur between 170 and 220 K from numerous neutron-scattering experiments and MD simulations to—see e.g., [ 29 , 30 , 31 ] for recent references. Note however that the nature of this transition is still heavily debated.…”

Structural properties of supercooled deep eutectic solvents: choline chloride–thiourea compared to reline

“…34,35 It was shown that these motions participate in the collective motion of the surroundings 35 and are determined by the nearest nanoscale surrounding of the spin-labeled molecule. 37–39 On these grounds, these motions may deliver unique information on the rigidity of nanoscale molecular packing in the molecular systems under study. Except for the mentioned above ILs, nanoscale molecular packing was studied with pulsed EPR for model biological membranes (lipid bilayers) 37–42 and for proteins.…”