Enhanced dynamics in the anomalous melting regime of DMPG lipid membranes

Abstract

Like many soft materials, lipids undergo a melting transition associated with a significant increase in their dynamics. At temperatures below the main melting transition ( T m ), all molecular and collective dynamics are suppressed, while above T m the alkyl tail motions, lipid diffusivity, and collective membrane undulations are at least an order of magnitude faster. Here we study the collective dynamics of dimyristoylphosphatidylglycerol (DMPG, di 14:0 PG) using neutron spin echo spectroscopy throughout its anomalous phase transition that occurs over a 12 °C–20° C wide temperature window. Our results reveal that the membranes are softer and more dynamic during the phase transition than at higher temperatures corresponding to the fluid phase and provide direct experimental evidence for the predicted increase in membrane fluctuations during lipid melting. These results provide new insights into the nanoscale lipid membrane dynamics during the melting transition and demonstrate how these dynamics are coupled to changes in the membrane structure.

Lateral diffusion of lipids in the DMPG membrane across the anomalous melting regime: effects of NaCl

“…In the case of unextruded DMPG vesicles, a sharp peak is observed just around T on m , which is absent in the present case of extruded DMPG vesicles. 19,20 Our DSC data profile is very similar to the reported DSC profile for the extruded vesicles, though at a different concentration. 20 As shown in Fig.…”

“…19,20 Our DSC data profile is very similar to the reported DSC profile for the extruded vesicles, though at a different concentration. 20 As shown in Fig. 1(a), it is evident that the DSC thermogram for the DMPG membrane in the presence of 100 mM NaCl is starkly different compared to that of the pure DMPG membrane, indicating that the presence of NaCl modulates the phase behaviour of the DMPG membrane.…”

“…No unusual (e.g., faster than in the fluid phase) lateral diffusion is observed in the intermediate phase or during the phase transition, in contrast to the reported enhanced collective motion of the DMPG membrane during the phase transition (or in the intermediate phase) compared to the high temperature fluid phase. 20 Viscosity measurements for the DMPG membrane in the low ionic strength solvents show an anomalous peak-like behaviour. 18 In the transition regime, the viscosity of DMPG vesicles is about 10 times higher than that observed in the ordered and fluid phase.…”

“…High viscosity in the intermediate region has been explained based on the increase in the size and ionization of the vesicles. 12,18,19 Recent neutron spin echo measurements 20 have shown that during the phase transition membranes are softer and more dynamic compared to the higher temperature fluid phase. This is a very interesting direct observation on the enhanced bending fluctuation of the membrane during the melting regime.…”

Small-Angle Neutron Scattering for Studying Lipid Bilayer Membranes

“…More novel lipids have been studied using SANS, such as fully artificial ones [ 144 ] and siloxane phosphocholines [ 145 ]. SANS also provides the important membrane thickness needed for understanding the dynamics of lipid bilayers that have been measured by NSE [ 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 , 154 ], although the information reported about the structure may not be as detailed as what is found in a study dedicated to membrane structure.…”