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Figure 2.
Figure 2. Similarities between the Catalytic Domains of
Rel[Seq], Human Phosphodiesterase (PDE) and Human DNA Polymerase
Beta (pol β)Structural and topological diagrams highlighting
equivalent folds and active-site residues for: (A) catalytic
domain (residues 152−528) of PDE4; (B) Rel[Seq]1–385; (C)
catalytic domain (residues 10−335) of pol β. Homologous
structural elements are displayed as ribbons; nonequivalent
regions as thin gray lines. Monomer 2 of Rel[Seq]1–385 is
shown, with ppG2′:3′p, and GDP. Dark blue sphere,
catalytic metal ion (Zn^2+ for PDE4; Mn^2+ for Rel[Seq]).
Conserved residues of the H−X[(n)]−HD−X[(n)]−D metal
binding tetrad are labeled in the accompanying topology diagrams
(A and B). Two of the three catalytic carboxylates in pol β
(Asp190 and Asp256, C) are also found in Rel[Seq] (Asp264 and
Glu323, B). Rel/Spo enzymes lack a counterpart for the second
carboxylate of the D-X-D motif in NTases (Asp192 in pol β).
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