Dataset Information

Rate of steroid double-bond reduction catalysed by the human steroid 5?-reductase (AKR1D1) is sensitive to steroid structure: implications for steroid metabolism and bile acid synthesis.

ABSTRACT: Human AKR1D1 (steroid 5?-reductase/aldo-keto reductase 1D1) catalyses the stereospecific reduction of double bonds in ?4-3-oxosteroids, a unique reaction that introduces a 90° bend at the A/B ring fusion to yield 5?-dihydrosteroids. AKR1D1 is the only enzyme capable of steroid 5?-reduction in humans and plays critical physiological roles. In steroid hormone metabolism, AKR1D1 serves mainly to inactivate the major classes of steroid hormones. AKR1D1 also catalyses key steps of the biosynthetic pathway of bile acids, which regulate lipid emulsification and cholesterol homoeostasis. Interestingly, AKR1D1 displayed a 20-fold variation in the kcat values, with steroid hormone substrates (e.g. aldosterone, testosterone and cortisone) having significantly higher kcat values than steroids with longer side chains (e.g. 7?-hydroxycholestenone, a bile acid precursor). Transient kinetic analysis revealed striking variations up to two orders of magnitude in the rate of the chemistry step (kchem), which resulted in different rate determining steps for the fast and slow substrates. By contrast, similar Kd values were observed for representative fast and slow substrates, suggesting similar rates of release for different steroid products. The release of NADP+ was shown to control the overall turnover for fast substrates, but not for slow substrates. Despite having high kchem values with steroid hormones, the kinetic control of AKR1D1 is consistent with the enzyme catalysing the slowest step in the catabolic sequence of steroid hormone transformation in the liver. The inherent slowness of the conversion of the bile acid precursor by AKR1D1 is also indicative of a regulatory role in bile acid synthesis.

SUBMITTER: Jin Y

PROVIDER: S-EPMC4163838 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Rate of steroid double-bond reduction catalysed by the human steroid 5β-reductase (AKR1D1) is sensitive to steroid structure: implications for steroid metabolism and bile acid synthesis.

Jin Yi Y Chen Mo M Penning Trevor M TM

The Biochemical journal 20140801 1

Human AKR1D1 (steroid 5β-reductase/aldo-keto reductase 1D1) catalyses the stereospecific reduction of double bonds in Δ4-3-oxosteroids, a unique reaction that introduces a 90° bend at the A/B ring fusion to yield 5β-dihydrosteroids. AKR1D1 is the only enzyme capable of steroid 5β-reduction in humans and plays critical physiological roles. In steroid hormone metabolism, AKR1D1 serves mainly to inactivate the major classes of steroid hormones. AKR1D1 also catalyses key steps of the biosynthetic pa ...[more]

PMID: 24894951

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Project description:Steroid hormones, including glucocorticoids and androgens, exert a wide variety of effects in the body across almost all tissues. The steroid A-ring 5β-reductase (AKR1D1) is expressed in human liver and testes, and three splice variants have been identified (AKR1D1-001, AKR1D1-002, AKR1D1-006). Amongst these, AKR1D1-002 is the best described; it modulates steroid hormone availability and catalyses an important step in bile acid biosynthesis. However, specific activity and expression of AKR1D1-001 and AKR1D1-006 are unknown. Expression of AKR1D1 variants were measured in human liver biopsies and hepatoma cell lines by qPCR. Their three-dimensional (3D) structures were predicted using in silico approaches. AKR1D1 variants were overexpressed in HEK293 cells, and successful overexpression confirmed by qPCR and Western blotting. Cells were treated with either cortisol, dexamethasone, prednisolone, testosterone or androstenedione, and steroid hormone clearance was measured by mass spectrometry. Glucocorticoid and androgen receptor activation were determined by luciferase reporter assays. AKR1D1-002 and AKR1D1-001 are expressed in human liver, and only AKR1D1-006 is expressed in human testes. Following overexpression, AKR1D1-001 and AKR1D1-006 protein levels were lower than AKR1D1-002, but significantly increased following treatment with the proteasomal inhibitor, MG-132. AKR1D1-002 efficiently metabolised glucocorticoids and androgens and decreased receptor activation. AKR1D1-001 and AKR1D1-006 poorly metabolised dexamethasone, but neither protein metabolised cortisol, prednisolone, testosterone or androstenedione. We have demonstrated the differential expression and role of AKR1D1 variants in steroid hormone clearance and receptor activation in vitro. AKR1D1-002 is the predominant functional protein in steroidogenic and metabolic tissues. In addition, AKR1D1-001 and AKR1D1-006 may have a limited, steroid-specific role in the regulation of dexamethasone action.

Dataset Information

Rate of steroid double-bond reduction catalysed by the human steroid 5?-reductase (AKR1D1) is sensitive to steroid structure: implications for steroid metabolism and bile acid synthesis.

Publications

Rate of steroid double-bond reduction catalysed by the human steroid 5β-reductase (AKR1D1) is sensitive to steroid structure: implications for steroid metabolism and bile acid synthesis.

Similar Datasets

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