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as the softness of the cell membrane and diffusion dynamics, which seem
to occlude imaging of individual membrane molecules on a cell, at least in
the near future. To date, we have been able to image native membranes
ex cellula
, which means that minimal biochemical treatments have been
employed (cell breakage and density gradient centrifugation) to isolate
membranes from other cellular constituents.
Figure 2.2.
The nativeness of studied samples from left (less native) to the right (more
native): membrane protein 3D crystal, membrane protein 2D crystal, densely packed
reconstitution, loosely packed reconstitution, native membrane
ex cellula
and native
membrane
in cellula
.
This chapter focuses on the imaging of proteins in native membranes by
AFM, taking advantage of its capability to image single molecules in native
samples. We will discuss the examples of AFM where novel information
about molecular variability and supramolecular assemblies of membrane
proteins, not analysable by any other technique to date, has been presented.
The following sections focus on the studies about prokaryotic photosynthetic
membranes and on the characterization of eukaryotic eye lens membranes.
Finally, the power of the recently introduced high-speed AFM (HS-AFM) for
biomembrane research is evidenced.
2.2 HIGHRESOLUTION AFM IMAGING OF PROKARYOTIC
MEMBRANES
The application of AFM in imaging membrane proteins has been successful in
two-dimensional (2D) reconstituted systems, i.e., water channel aquaporin Z,
3
potassium channel KirBac3.1,
4
halorhodopsin,
5
outer membrane (OM) porins,
6
ATP synthase (ATPase)
7-12
and light-harvesting complexes.
13-17
Proteins of
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