Young modulus of supported lipid membranes containing milk sphingomyelin in the gel, fluid or liquid ordered phase, determined using AFM force spectroscopy
Résumé
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 continuous
lipid phase. The objective of this study was to investigate whether changes in the phase state of milk SM-rich
domains induced by temperature (T < Tm or T > Tm) or cholesterol affected the Young modulus of the lipid
membrane. 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 Young
modulus values of 10–20 MPa and 4–6 MPa, respectively. Upon heating at 50 °C, the milk SM-rich domains in
MFGM bilayers as well as pure milk SM bilayers melted, leading to the formation of a homogeneous membrane
with similar Young modulus values to that of a fluid phase (0–5 MPa). Upon addition of cholesterol to the milk
SM 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 the
Young modulus was weakly affected by the temperature. These results open perspectives for the development of
milk polar lipid based vesicles with modulated mechanical properties.
Origine : Accord explicite pour ce dépôt
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