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Figure 5.
Figure 5. Stereo views of the heme group environment in
SCC-A. (a) side heme view and (b) view perpendicular to the heme
plane. Carbon, oxygen and nitrogen atoms are represented as
open, shaded and filled spheres, respectively. Hydrogen bonds
are indicated by broken lines. The heme group, the azide
molecule found in the distal side, the essential catalytic
residues (His70, Ser109, Asn143, Arg351 and Tyr355), and two
water molecules which are hydrogen-bonded to the propionic
groups are explicitly shown in (a). The deprotonated oxygen of
Tyr355, that makes two ionic hydrogen bonds with Arg351, acts as
the proximal ligand of the iron atom (coordination is also
indicated with a discontinuous bond). Residues that define the
heme distal pocket are explicitly shown in (b). Asn68 interacts
with Asp62 from the R related subunit (indicated by the symbol *
in the Figure) and with a solvent molecule which starts a chain
of water molecules that reach the central cavity of the catalase
molecules (see the text). Neither the main-chain oxygen atom of
cis-Pro69 nor the side-chain oxygen atom of Asn143 form standard
hydrogen bonds and might interact with the heme ring.
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