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Figure 2.
Figure 2: The APO2 active site. a, The APO2 active sites are
accessible to DNA/RNA. Red spheres represent Zn. b, The fntCDA
active site is accessible only to free nucleotides. c, The outer
APO2 active sites show Zn coordination (yellow dashed lines) by
three residues (H98, C128, C131) and a water molecule (blue
sphere). d, The middle APO2 active centre sites show Zn
coordination by a fourth residue, E60. e, In the  1'-hairpin
structure, the hydrophobic ring of Y61 interacts with the
guanidine group of R65, stabilizing the conformation. f, In the
h1/ 1
loop, the E60 coordinates with Zn. Y61 now rotates away from R65
and interacts with R57, facilitating the disruption of the 1'-hairpin
and stabilizing the loop conformation. g, Superimposed monomers
show that the h1/ 1
loop (purple) is pulled down  8.5
Å towards the active site owing to the E60–Zn bond
formation.
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