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![[Figure 4]](ud5010fig4mag.jpg)
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Figure 4
The Q123D design (green; PDB entry 6u0x) predicts the correct interaction type but the incorrect interaction residue. In the design, Asp123 is predicted to form an electrostatic interaction with Lys71′ (where the prime indicates the symmetry mate), improving on the WT Gln–Lys interaction (pale yellow). However, this interaction is missing in the density and crystal structure of the variant (both orange; the 2mFo − DFc map contoured at 1.5σ for the Q123D variant crystal structure is carved within 2 Å of residues 71, 84 and 123). In place of the Glu123–Lys71 interaction, Asp123 hydrogen-bonds to Lys84, which also noncovalently interacts with the nucleotide analog (thymidine-3′,5′-diphosphate; THP) bound in the SNase active site. In this figure, each residue belongs to either the asymmetric unit or a different symmetry mate. Key interactions with atom-pair distances less than 3.5 Å are shown as dashed lines. |
![[Figure 4]](ud5010fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
