1482-51-5Relevant articles and documents
The effect of disease associated point mutations on 5β-reductase (AKR1D1) enzyme function
Mindnich, Rebekka,Drury, Jason E.,Penning, Trevor M.
scheme or table, p. 250 - 254 (2012/03/26)
The stereospecific 5β-reduction of Δ4-3-ketosterols is very difficult to achieve chemically and introduces a 90° bend between ring A and B of the planar steroid. In mammals, the reaction is catalyzed by steroid 5β-reductase, a member of the aldo-keto reductase (AKR) family. The human enzyme, AKR1D1, plays an essential role in bile-acid biosynthesis since the 5β-configuration is required for the emulsifying properties of bile. Deficient 5β-reductase activity can lead to cholestasis and neo-natal liver failure and is often lethal if it remains untreated. In five patients with 5β-reductase deficiency, sequencing revealed individual, non-synonymous point mutations in the AKR1D1 gene: L106F, P133R, G223E, P198L and R261C. However, mapping these mutations to the AKR1D1 crystal structure failed to reveal any obvious involvement in substrate or cofactor binding or catalytic mechanism, and it remained unclear whether these mutations could be causal for the observed disease. We analyzed the positions of the reported mutations and found that they reside in highly conserved portions of AKR1D1 and hypothesized that they would likely lead to changes in protein folding, and hence enzyme activity. Attempts to purify the mutant enzymes for further characterization by over-expression in Escherichia coli yielded sufficient amounts of only one mutant (P133R). This enzyme exhibited reduced Km and kcat values with the bile acid intermediate Δ4-cholesten-7α- ol-3-one as substrate reminiscent of uncompetitive inhibition. In addition, P133R displayed no change in cofactor affinity but was more thermolabile as judged by CD-spectroscopy. When all AKR1D1 mutants were expressed in HEK 293 cells, protein expression levels and enzyme activity were dramatically reduced. Furthermore, cycloheximide treatment revealed decreased stability of several of the mutants compared to wild type. Our data show, that all five mutations identified in patients with functional bile acid deficiency strongly affected AKR1D1 enzyme functionality and therefore may be causal for this disease.
REDUCTIONS MICROBIOLOGIQUES STEREOSELECTIVES DES Δ-4 CETO-3 STEROIDES
Fauve, A.,Kergomard, A.
, p. 899 - 901 (2007/10/02)
In anaerobic conditions the reduction of Δ-4 3-keto steroids by Clostridium paraputrificum leads either to the 3-keto 5β compounds or to the corresponding 3α-hydroxytetrahydro-5β derivatives.This stereospecific bioconversion of αβ-unsaturated 3-keto steroids is shown to be directed by the substrate concentration.The conversion of Δ-4 cholestenone to coprostanone or coprostanol is not observed.
