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Figure 3.
Figure 3. Hexameric Ring Model of the FtsH ATPase Domain(A)
The figures are viewed from the transmembrane side (left) and
the protease domain side (right). From the extra segment
position of the FtsH-F2 crystal structure, we found that the
transmembrane helices are located on the N-terminal side of the
hexagonal plate. The model possesses an outer diameter of
approximately 120 Å, with a central pore of 13 Å in diameter.
Note the gap between subunits, which becomes narrow in
comparison with that in the crystal packing arrangement, as
shown in Figure 1D. The rotation angle between subdomains in the
model differs by 34° from that in the crystal. Although every
subunit is represented with the same conformation in this model,
the mode of the ATPase cycle, either sequential or synchronized,
cannot be clarified.(B) Representation of the arginine finger in
the model viewed from the transmembrane side. Arg313 is located
at a position capable of interacting with the g-phosphate of
AMP-PNP bound to a neighboring subunit. The SRH motif,
highlighted in pink, is located on the contact surface between
subunits. The a7 helix and the following loop in front of Arg313
are eliminated.(C) SRH motif in the model, viewed from the
protease domain side. The motif from the AMP-PNP form is
superimposed onto that from the ADP form. The Ca atom of Asn302
is colored red.(D) Mapping of the putative substrate binding
regions (brown). Note that the MFVG sequence (green) faces the
central pore. A closed line indicates a monomer structure,
corresponding to the highlighted one in (A).(E) Electrostatic
potential surfaces of the model, calculated by the program GRASP
[52]. Red and blue represent regions of negative and positive
potential, respectively.
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