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Figure 3.
Figure 3. The Domain Interface and Heme Binding Sites of
Pap Cytochrome c Peroxidase
(A) Domain interface of the
oxidized Pap CCP looking down at the noncrystallographic 2-fold
axis. Color code is the same as used in Figure 1 and Figure 2.
The hemes, the calcium ion, and some key residues in the Pap
structures are in ball-and-stick representation.
(B) Domain
interface of the mixed valence form Pap CCP shown as in Figure
3A.
(C) Close view of the peroxidatic heme site and dimer
interface of the mixed valence form of Pap CCP. The loop
carrying His85 moves away to the interface of the homodimer.
This structure is stabilized by p-stacking interaction between
the aromatic side chain of Trp87 and the peptide bond of Gly72
of the opposite chain (labeled as G72B). The peroxide binding
site is occupied by a water molecule, which is hydrogen bonded
to Gln118 and Glu128. The corresponding residues in the oxidized
form are shown in red.
(D) Stereoview of the
electron-transferring heme of the mixed valence form of Pap CCP.
The propionate D group of the heme undergoes a conformational
change upon reduction and loses the interaction with the main
chain amide of Leu230. The corresponding conformation in the
oxidized form is shown in red. The SIGMAA (Read, 1986) weighted
2mF[o] - DF[c] electron density using phases from the final
model of the half-reduced form is contoured at 1.5 s level,
where s represents the rms electron density for the unit cell.
Contours more than 1.4 Å from any of the displayed atoms have
been removed for clarity. Thin lines indicate hydrogen bonds.
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