Unsaturated lipid bilayers at cryogenic temperature: librational dynamics of chain-labeled lipids from pulsed and CW-EPR

Abstract

Echo-detected EPR spectra are used to study the effects of acyl chain unsaturation on the librational motion of chain-labeled lipids in the low-temperature phases of POPC and DOPC bilayers.

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

“…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.…”

“…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 ]. This result is consistent with that observed here in Figure 4 for casein.…”

“…This result is consistent with that observed here in Figure 4 for casein. However, for the spin label in the interior of the DOPC bilayer [ 28 ] (the label is at the 16th carbon position of the acyl chain), the starting temperature of the increase is diminished down to 160 K, which implies that in the DOPC bilayer interior the motions become too intensive to be compared with those in casein.…”

“…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

“…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. 34,43–45…”