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![[Figure 3]](chr5006fig3mag.jpg)
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Figure 3
Location of the changes in HbHNL to make increasingly large regions surrounding the active site identical in sequence to the esterase SABP2. (a) Ribbon diagram of HbHNL (PDB entry 1yb6) showing the locations of changes introduced into HbHNL to create HNL16. The lid domain (sky blue, 108–181) lies at the top and front, while the catalytic domain (light gray, 1–107 and 182–257) lies in the lower and deeper parts in this view. The catalytic triad Ser–His–Asp (side chains shown as green sticks) lies in the catalytic domain at the interface between the two domains. The HbHNL substrate mandelonitrile (blue sticks) lies in the active site. HNL16 contains 16 substitutions at the locations marked by black spheres. These changes make the amino-acid residues in HNL16 identical to those in SABP2 in a region surrounding the substrate by ∼6.5 Å. (b) Ribbon diagram of chain A of HNL40 (PDB entry 8sni) showing the locations of changes introduced into HbHNL to create HNL40 and HNL71. The HNL40 set includes the substitutions in HNL16. A bound L-proline (blue sticks) lies in the substrate-binding region and mimics the product carboxylate of an ester hydrolysis. Both HNL40 and HNL71 include two insertions (rose spheres) after residue 126 of HbHNL and the 38 substitutions marked as dark orange spheres. These changes in HNL40 make the protein sequence of the region within 10 Å of the substrate-binding site identical to that in SABP2. HNL71 contains 31 additional substitutions (yellow spheres) to make the protein sequence of the region within 14 Å identical to that in SABP2. In the HNL71 structure, the electron density was insufficient to define the positions of nine surface-exposed amino-acid residues: 142–143 (lid domain) and 182–188 (catalytic domain). These regions were defined in the HNL40 structure shown and are circled in red. In HNL71, the side chain of Cys163 (sticks) is oxidized to the sulfenic acid. |
![[Figure 3]](chr5006fig3.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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