Biomedical Engineering Reference
In-Depth Information
6.4 nm
20
6.3 nm
10
6.2 nm
1 µm
5.2 nm
0
0
1
2
3
4
5
Distance / µm
Topography
A
B
500 nm
Topography
Friction
Phase
C
D
500 nm
Fig. 7.22. Examples of bilayer structural studies. Top: demonstration of the influence of the
substrate surface on bilayer height. The four layers are identical in composition, but the one next
to the substrate appears considerably thinner. Below: differentiating phases in phospholipid mixtures
by LFM and phase imaging. Left: topography (A,C) and LFM (B,D) of a mixture of DSPE and
DOPE. The monolayers were imaged in air (A,B) and under liquid (C,D). Right: phase imaging of
E.
coli
total extract in liquid. Note that there are several different lipids in this mixture, and some are
discriminated by phase imaging, while others are not. Reproduced with permission from [129] (top),
and [652] (left).
simply fusing proteolipsomes instead of liposomes onto a mica surface [308]. The
protrusion of the membrane proteins above the flat lipid surface can then be imaged
directly, and can give important information about protein insertion, see for instance the
example on the left of Figure 7.23. Lipid membranes have also been used as a scaffold to
study the fine structure of membrane protein oligomers in their native state. In AFM,
membrane proteins have been widely studied in 2-D crystals, which are a highly stable
configuration, allowing high-resolution imaging [320]. However such systems do not very
closely represent the native conditions for membrane proteins. On the other hand, incorp-
oration of protein complexes into membranes allows their imaging in conditions much
closer to the native ones, and can demonstrate different structures to those found in the
