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Figure 3.
Figure 3. Comparison of 3'-5' exonuclease active sites.
Stereo diagram of the BF polymerase vestigial exonuclease active
site (red) with the position of a portion of the structure of
the KF active site (gold) [4] superimposed. The KF Ca backbone
schematic is accompanied by is two bound zinc atoms (green), and
three nucleotides (black) from the KF editing complex [11]. The
KF residues shown (yellow) are the four residues that bind the
two metal ions essential for catalysis. These essential KF
sidechains Asp355, Glu357, Asp424, and Asp501 correspond to BF
residues Val319, Glu321, Ala376, and Lys450, respectively (shown
in blue). Also shown in blue are two BF proline residues (438
and 441) that may be responsible for the collapse of a loop
between helices E[1] and F (dotted line) into the exonuclease
cleft not observed in KF. (Drawn with RIBBONS [71].)
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