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the recent success in structural studies of most components of the ATP
synthase, the supramolecular assembly of ATP synthases in biological
membranes remains unclear. A number of indirect studies indicated the
importance of subunits
for ATP synthase dimerization. 61,62 Also
the so-called inhibitory factor peptide IF1 was shown to interact with ATP
synthase dimers. 63,64 AFM was used to investigate native inner mitochondrial
membranes from yeasts and, with submolecular resolution, showed the
supramolecular organization of ATP synthases.
The AFM images showed mica-adsorbed lipid bilayers with embedded
ring-shaped molecules with characteristic diameter of ~8 nm. These objects
were identiied as ATP synthase c-rings, viewed on the periplasmic surface
of the inner mitochondrial membrane ( Fig. 2.7a ) . 65 ATP synthase molecules
form dimers with characteristic 15 nm distance between the rotor axes
through stereospeciic interactions of the membrane-embedded portions of
their stators ( Figs. 2.7b and 2.7c ) . According to this model, the surfaces of
subunits
e
and
g
plays
a role in the formation of rows of dimers. Such an organization reinforces
the role of the ATP synthase in mitochondrial morphology, where the sterical
mismatch of F 0 and F 1 parts would create the membrane curvature and thus
contribute to the formation of mitochondrial cristae. 62 Some ATP synthase
dimers have 10 nm stalk-to-stalk distance, interpreted as ATP synthases that
are accessible to IF1 inhibition. Existence of mitochondrial ATP synthases in
functional rows dimers was supported by cryo-tomography studies. 66
e
and
g
are responsible for dimer formation while subunit
b
(a)
(b)
(c)
Figure 2.7. Supramolecular organization of ATP synthases in native mitochondrial
inner membranes. (a) Topograph of mica-adsorbed inner mitochondrial membrane
with rows of ATP synthases. (b) High-resolution image of ATP synthase dimers
(outlined). Dimer with intermolecular distances of 15 nm and 10 nm are marked with
white and yellows arrows, respectively. (c) Schematic representation of dimer and
oligomer assembly.
 
 
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