Young modulus of supported lipid membranes containing milk sphingomyelin in the gel, fluid or liquid ordered phase, determined using AFM force spectroscopy
2019
Guyomarc'h, Fanny | ET THAKAFY, Oumaima | Lopez, Christelle
The biological membrane surrounding milk fat globules (MFGM) exhibits lateral phase separation of lipids,interpreted as gel or liquid-ordered phase sphingomyelin-rich (milk SM) domains dispersed in a fluid continuouslipid phase. The objective of this study was to investigate whether changes in the phase state of milk SM-richdomains induced by temperature (T < Tm or T > Tm) or cholesterol affected the Young modulus of the lipidmembrane. Supported lipid bilayers composed of MFGM polar lipids, milk SM or milk SM/cholesterol(50:50 mol) were investigated at 20 °C and 50 °C using atomic force microscopy (AFM) and force spectroscopy.At 20 °C, gel-phase SM-rich domains and the surrounding fluid phase of the MFGM polar lipids exhibited Youngmodulus values of 10–20 MPa and 4–6 MPa, respectively. Upon heating at 50 °C, the milk SM-rich domains inMFGM bilayers as well as pure milk SM bilayers melted, leading to the formation of a homogeneous membranewith similar Young modulus values to that of a fluid phase (0–5 MPa). Upon addition of cholesterol to the milkSM to reach 50:50 mol%, membranes in the liquid-ordered phase exhibited Young modulus values of a few MPa,at either 20 or 50 °C. This indicated that the presence of cholesterol fluidized milk SM membranes and that theYoung modulus was weakly affected by the temperature. These results open perspectives for the development ofmilk polar lipid based vesicles with modulated mechanical properties.
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