HIGH-RESOLUTION ATOMIC FORCE MICROSCOPY OF NATIVE MEMBRANES - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 25

The hexagonally packed intermediate (HPI) layer in Deinococcus

radiodurans is another typical bacterial S-layer. 32,33 There are six identical

protomers that form the HPI layer pore, and unplugged and plugged
conformations have been observed. High-resolution AFM images, together
with manipulation, exhibit both outer and inner layer surface ( Fig. 2.3d ).
The outer surface of the HPI layer is a hexagonal lattice with a unit cell
size of 18 nm ( Fig. 2.3e ) . 34,35 This arrangement presents relatively large
openings around the six-fold axes. The inner surface of the HPI layer shows
conformational dynamics of pores: a “closed” pore with a central plug and an
“open” pore without it ( Fig. 2.3f ). 35 On both S-layers from C. glutamicum and

D. radiodurans force measurements have been performed. 20,32,36

(a) (b) (c)

(d) (e) (f)

Figure 2.3. (a) Nano-dissection of the top outer surface of the S-layer of
Corynebacterium glutamicum using AFM (1), providing access to the bottom S-layer
and revealing the topography of the inner surface (2) of C. glutamicum. 20 (b) High-
resolution topograph of the outer S-layer surface of (inset: average).

(c) High-resolution topograph of the inner S-layer surface (inset: average). (d) Nano-
dissection and high-resolution imaging of S-layers of Deinococcus radiodurans using
AFM, showing the bottom outer surface of the S-layer (1) and the top S-layer which
exposes the inner surface (2) of D. radiodurans. 32,33 (e) High-resolution topograph of
the outer S-layer surface of

C. glutamicum

. The high imaging contrast allows detection
of the substructure on each individual subunit, revealing V-shaped units with a slight
left-handed twist (inset: average). (f ) High-resolution topograph of the inner S-layer
surface of D. radiodurans .

D. radiodurans

Furthermore, the possibility to image the S-layer in vivo without invasive

sample preparation has been proved. More recently, Dupres and co-

workers have made great effort in visualizing S-layer nanoarrays on living

37

C.

glutamicum high-resolution imaging is signiicant

in understanding the structure of protein monomolecular arrays in their
native state.

bacterial cells.

38

The in situ