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Mutations of human cytochrome P450 reductase differentially modulate heme oxygenase-1 activity and oligomerization

Christopher C Marohnic1, Warren J Huber Iii, J Patrick Connick

  • 1The University of Texas Health Science Center at San Antonio, Department of Biochemistry, USA. masters@uthscsa.edu

Archives of Biochemistry and Biophysics
|July 12, 2011
PubMed

Insights

Genetic variations in NADPH-cytochrome P450 oxidoreductase (CYPOR) diminish heme degradation by heme oxygenase-1 (HO-1). Different CYPOR variants show varying impacts on HO-1 activity, potentially complicating CYPOR deficiency.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Genetics

Background:

  • Genetic variations in POR, encoding NADPH-cytochrome P450 oxidoreductase (CYPOR), affect numerous cytochrome P450 functions.
  • These variations can also impede the degradation of heme by heme oxygenase-1 (HO-1).

Purpose of the Study:

  • To investigate the impact of naturally occurring human CYPOR variants on heme degradation by HO-1.
  • To characterize the interaction between CYPOR variants and HO-1, including binding affinities and optimal ratios.

Main Methods:

  • Purified human CYPOR variants, HO-1, and biliverdin reductase were reconstituted in lipid vesicles.
  • Assays measured NADPH-dependent conversion of heme to bilirubin for wild-type (WT) and variant CYPOR.
  • The effect of FMN, FAD, and varying CYPOR:HO-1 ratios on activity was examined.

Main Results:

  • All tested CYPOR variants showed reduced bilirubin production compared to WT, indicating diminished HO-1 activity.
  • Apparent affinity of the CYPOR-HO-1 complex was lower for variants than WT.
  • FMN or FAD partially restored activity for specific variants (Y181D, Y459H, V492E).
  • Only the Y181D variant inhibited HO-1 activity by sequestering it, suggesting differential binding affinities among variants.
  • Optimal CYPOR:HO-1 ratio for activity was 1:2, supporting HO-1 oligomerization.

Conclusions:

  • Human POR mutations lead to varying degrees of diminished HO-1 activity.
  • These findings suggest that CYPOR variants have differential binding affinities with redox partners.
  • The impact on HO-1 activity may further complicate the clinical presentation of CYPOR deficiency.

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