Biology Reference
In-Depth Information
technique was already able to study the organization of raft-like systems.
73
The ability of AFM to explore biological membranes should also beneit from
its coupling to other techniques such as polarized total internal relection
luorescence microscopy. Using such combination, it was possible to evaluate
membrane order parameters and to track changes in lipid headgroup and
acyl chain reordering in SLBs, while simultaneously resolving molecular-
scale topographical changes.
74
Progress in the development of non-contact mode AFM, mainly frequency
modulation (FM)-AFM, is also expected. Here, the cantilever is excited at
ixed amplitude and the topography followed by keeping the frequency
modulation constant. FM-AFM imaging in liquid was achieved on SLBs
75
or
purple membranes.
76
It could be implemented in commercial setups but
still needs further improvement to better control tip-sample interactions,
especially with corrugated samples where adhesion events largely perturb
the detection of frequency shifts. Another non-destructive approach, called
scanning near-ield ultrasonic holography or ultrasonic force microscopy, is
currently under development. It uses high-frequency oscillators to generate
spatially resolved images. In collaboration with Lesniewska's group, we could
observe lipid phase separation within SLBs using this approach.
1.8 CONCLUSION
AFM represents a irst-choice technique in the study of SLBs, allowing the
topography of membrane components to be acquired at (sub)molecular
resolution under physiological conditions. Particular attention has to be
paid to the choice of lipids to mimic biological membranes as well as to
experimental conditions used for lipid vesicles adsorption and fusion. Major
advances in the understanding of membrane components partitioning into
microdomains have been achieved with AFM. Moreover, this technique
can also be useful in delineating the structure of membrane proteins. We
can speculate that future technical improvements of AFM techniques will
contribute to their broader use in biomembrane research.
Acknowledgements
This work was supported by institutional grants from INSERM and CNRS and
by speciic grants from the French research agency ANR (PCV08-AFM-MB-
PROT, PCV08_343399 and 08-NANO-010).
Search WWH ::
Custom Search