Structure and catalytic mechanism of human steroid 5beta-reductase (AKR1D1).
Human steroid 5beta-reductase (aldo-keto reductase (AKR) 1D1) catalyzes reduction of Delta(4)-ene double bonds in steroid hormones and bile acid precursors. We have reported the structures of an AKR1D1-NADP(+) binary complex, and AKR1D1-NADP(+)-cortisone, AKR1D1-NADP(+)-progesterone and AKR1D1-NADP(+)-testosterone ternary complexes at high resolutions. Recently, structures of AKR1D1-NADP(+)-5beta-dihydroprogesterone complexes showed that the product is bound unproductively. Two quite different mechanisms of steroid double bond reduction have since been proposed. However, site-directed mutagenesis supports only one mechanism. In this mechanism, the 4-pro-R hydride is transferred from the re-face of the nicotinamide ring to C5 of the steroid substrate. E120, a unique substitution in the AKR catalytic tetrad, permits a deeper penetration of the steroid substrate into the active site to promote optimal reactant positioning. It participates with Y58 to create a "superacidic" oxyanion hole for polarization of the C3 ketone. A role for K87 in the proton relay proposed using the AKR1D1-NADP(+)-5beta-dihydroprogesterone structure is not supported.
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Luigi
L
Di Costanzo
Jason E
JE
Drury
David W
DW
Christianson
Trevor M
TM
Penning
D055162:Biocatalysis; D006801:Humans; D006860:Hydrogen Bonding; D016018:Least-Squares Analysis; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D017434:Protein Structure, Tertiary
D011374:Progesterone; D009249:NADP; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C100153:2,4-dienoyl-CoA reductase; C021936:3-oxo-5 beta-steroid delta 4-dehydrogenase