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principles of domain formation in artiicial membranes on eukaryotic plasma
membrane microdomains (for reviews, see Refs. 3, 7 and 36) or to interpret
detergent insolubility of microdomains in cells.
37
From numerous studies, it
was conirmed that Chl is a key component of the membrane organization
that interacts with saturated fatty acid chains of membrane lipids promoting
microdomain formation. However, discrepancies in publications were often
observed and could be explained by slight differences in the composition of the
lipid mixtures used. As an example, the physical properties of SLBs containing
SM can differ depending on whether synthetic lipids or natural (bovine brain)
lipids are used. In the latter case, SM fatty acid chains are heterogeneous in
length and in saturation. Consequently, a gel-to-luid transition occurs over a
broad range of temperature, including the physiological temperature, and a
gel-gel phase separation within SM domains using a SM/DOPC mixture has
(a)
(b)
Figure 1.3.
Imaging of sphingomyelin domains. (a) SLBs made of a mixture of SM
and DOPC (1:1) were observed using AFM contact mode in PBS buffer. SM can form
domains of different shapes, protruding from the darker DOPC luid phase: (a)
Corrugated domains formed by closely packed globular structures that protrude 5 nm
above the luid phase; (b) lat domains that protrude 1 nm above the luid phase. (b) is
the same area as the one in (a) observed after the addition of 5 mM CaCl
2
in the AFM
luid cell, meaning that the SM domain shape is dependent on divalent cations. The
z
scales in (a) and (b) are 50 and 10 nm, respectively. The scale bars are 1 μm.
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