Comparison of the crystal structure and function to wild-type and His25Ala mutant human heme oxygenase-1
Human heme oxygenase-1 (hHO-1) is a rate-limiting enzyme in heme metabolism. It regulates serum bilirubin level. Site-directed mutagenesis studies indicate that the proximal residue histidine 25 (His25) plays a key role in hHO-1 activity. A highly purified hHO-1 His25Ala mutant was generated and cry...
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Published in | International journal of molecular medicine Vol. 23; no. 3; pp. 379 - 387 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Greece
D.A. Spandidos
01.03.2009
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Subjects | |
Online Access | Get full text |
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Summary: | Human heme oxygenase-1 (hHO-1) is a rate-limiting enzyme in heme metabolism.
It regulates serum bilirubin level. Site-directed mutagenesis studies indicate
that the proximal residue histidine 25 (His25) plays a key role in hHO-1 activity.
A highly purified hHO-1 His25Ala mutant was generated and crystallized with a
new expression system. The crystal structure of the mutant was determined by X-ray
diffraction technology and molecular replacement at the resolution of 2.8 Å, and
the model of hHO-1 His25Ala mutant was refined. The final crystallographic and
free R factors were 0.245 and 0.283, respectively. The standard bond length deviation
was 0.007 Å, and the standard bond angle deviation was 1.3°. The mutation of His25
to Ala led to an empty pocket underneath the ferric ion in the heme, leading to
loss of binding iron ligand. Although this did not cause an overall structural
change, the enzymatic activity of the mutant hHO-1 was reduced by 90%. By supplementing
imidazole, the HO-1 activity was restored ≈90% to its normal level. These data
suggest that Ala25 remains unchanged in the structure compared to His25, but the
important catalytic function of hHO-1 is lost. Thus, it appears that His25 is
a crucial residue for proper hHO-1 catalysis. |
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ISSN: | 1107-3756 |
DOI: | 10.3892/ijmm_00000142 |