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Figure 5.
Figure 5. Subunit Interface in ClpP(A) The intra-ring
association of ClpP monomers is shown as a ribbon diagram.
Monomer 1 is shown in gray, monomer 2 in olive; residues in the
catalytic triad and those that stabilize the oxyanion
intermediate are represented as spheres: Ser-97 is magenta,
His-122 is green, Asp-171 is red, and Gly-68 and Met-98 are
olive. Dimerization of the two rings of heptamers results in the
formation of an antiparallel β sheet comprising strand 9 from
two NCS-related subunits. The small (+) represents the two-fold
axis relating the stacked monomers in opposing rings.(B) The
intraring contacts between monomers are shown; in one ring,
monomer 1 (gray) in (A) packs against monomer 3 shown in blue,
and in the opposing ring, monomer 2 (olive) in (A) packs against
monomer 4 shown in cyan. As in (A), the catalytic residues are
shown as spheres. As in (A), the small (+) represents the
location of the two-fold axis relating stacked monomers; the
large (+) represents the location of a second two-fold axis
that lies between each pair of interring subunits.(C) A CPK
representation of (B) showing the interdigitation of the
monomers.(D) A solvent-accessible surface representation of (B)
shows the connection between adjacent active site clefts in the
heptameric ring. The active sites in opposing heptamers are also
connected by channels that lie along the two-fold axes of the
oligomer, giving the surface of the proteolytic chamber a
zigzag-like appearance.(E) A schematic representation of two
putative models of substrate binding. Strands 9 are drawn as
unshaded arrows and heptapeptides as shaded arrows. Dashed lines
represent possible connections between hepta-peptides in a
continuous substrate. Residues in the catalytic triads are drawn
as spheres.(F) A longitudinal section of a space-filling model
colored according to hydrophobicity. The apical and outer
equatorial surfaces are enriched in charged residues, whereas
the inner surface of the chamber is largely hydrophobic. In
this representation, hydrophobic residues (Tyr, Phe, Leu, Ile,
Met, Val, Pro, and Ala) are colored in yellow, while charged
residues are colored in blue (Lys and Arg) and red (Asp and
Glu), respectively. All other residues are colored in gray.
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