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Figure 4.
Figure 4. Substrate binding to ADPRase. a, Location of the
two equivalent ADPR binding sites in the ADPRase dimer. In each
binding site, loop L8 of the opposite monomer is in close
proximity to the ribose moiety of ADPR. b, Stereo diagram of one
ADPR binding site. Residues of the two monomers contributing to
binding are labeled (B: main monomer, A: second monomer). The
2F[o] - F[c] electron density of the ADPR is shown in light
blue. Carbons are gray, oxygens red, nitrogens blue, phosphorous
yellow, and sulfur green; bound waters (labeled W3 and W4) are
shown as red spheres. The adenosine group of the substrate binds
to the enzyme in anti conformation (dihedral glycosylic bond is
-143°); the adenine ribose ring has C3'-endo puckering and the
terminal ribose binds with C2'-endo puckering. c, Interactions
between ADPR and ADPRase. The ADPR molecule is drawn with heavy
lines. Hydrogen bonds are shown with dashed blue lines; the
distances between donors and acceptors are indicated. Amino
acids providing van der Waals interactions are shown as
decorated arcs. Residue numbers are followed by a letter (A or
B) to indicate the monomer. Water molecules W1 to W4 are shown
as spheres.
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