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Structure-function of human 3 alpha-hydroxysteroid dehydrogenases: genes and proteins
T M Penning1, Y Jin, S Steckelbroeck
1Department of Pharmacology, University of Pennsylvania School of Medicine, 130C John Morgan Building, 3620 Hamilton Walk, Philadelphia, PA 19104-6084, USA. penning@pharm.med.upenn.edu
Molecular and Cellular Endocrinology
|March 18, 2004
Summary
Human 3 alpha-hydroxysteroid dehydrogenase (HSD) enzymes, part of the aldo-keto reductase (AKR) superfamily, exhibit functional plasticity. These enzymes may regulate key hormone receptors, with distinct tissue expression patterns observed.
Area of Science:
- Biochemistry
- Molecular Biology
- Endocrinology
Background:
- Four human 3 alpha-hydroxysteroid dehydrogenase (HSD) isoforms (AKR1C1-4) belong to the aldo-keto reductase (AKR) superfamily.
- These isoforms share high sequence identity (86%) and possess diverse enzymatic activities, including ketosteroid reductase and hydroxysteroid oxidase functions.
Purpose of the Study:
- To investigate the functional plasticity and structural basis of human 3 alpha-HSD isoforms (AKR1C1-4).
- To determine the in vivo activity and tissue-specific expression of AKR1C enzymes.
- To elucidate the potential role of AKR1C enzymes in regulating steroid hormone receptor occupancy.
Main Methods:
- Recombinant expression and in vitro enzymatic assays to determine kinetic parameters (kcat/Km).
- X-ray crystallography of AKR1C2 complexed with NADP+ and ursodeoxycholate.
- Transient transfection in COS-1 cells and RT-PCR for tissue expression analysis.
Main Results:
- Recombinant AKR1C enzymes exhibit broad substrate specificity and multiple activities.
- Crystal structure of AKR1C2 reveals ursodeoxycholate binding in an unusual orientation, explaining functional plasticity.
- In COS-1 cells, AKR1C enzymes primarily function as ketosteroid reductases due to NADPH inhibition of oxidase activity.
- AKR1C4 is liver-specific; AKR1C2 and AKR1C3 are predominantly expressed in prostate and mammary glands.
- AKR1C genes show conserved structure and potential regulation by steroid hormones and stress.
Conclusions:
- Human 3 alpha-HSD isoforms (AKR1C) display remarkable functional plasticity, influenced by cofactor availability and substrate binding orientation.
- These enzymes likely play significant roles in steroid hormone metabolism and receptor regulation.
- Discrete tissue-specific expression patterns suggest specialized functions for each AKR1C isoform in different organs.