PubMed · 11031991
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
Y Suzuki, N Shimozawa, A Imamura, N Kondo. 2000. [Peroxisomal disorders].. https://pubmed.ncbi.nlm.nih.gov/11031991/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
17beta-Hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the last step in the biosynthesis of all androgens and estrogens, thus playing a pivotal role in sex-hormone metabolism. Human 17beta-HSD type 5 (17beta-HSD5) catalyzes hydride transfer at the 17beta-hydroxy position, but possesses high sequence homology to 3alpha-hydroxysteroid dehydrogenases (3alpha-HSD). Two crystal forms of 17beta-HSD5 in an enzyme-testosterone-NADP ternary complex have been obtained under different crystallization conditions. A form I crystal obtained at pH 8.5 diffracted to 1.32 A. It belonged to space group P2(1), with unit-cell parameters a = 47.41, b = 77.16, c = 48.67 A, beta = 116.32 degrees. Form II crystals obtained at pH 6.5 diffracted to 2.0 A and belonged to space group P6(3), with unit-cell parameters a = b = 110.58, c = 56.89 A.
In this report, we reinvestigate the only patient ever reported with a deficiency of peroxisomal 3-ketoacyl-CoA thiolase (THIO). At the time when they were described, the abnormalities in this patient, which included accumulation of very-long-chain fatty acids and the bile-acid intermediate trihydroxycholestanoic acid, were believed to be the logical consequence of a deficiency of the peroxisomal beta-oxidation enzyme THIO. In light of the current knowledge of the peroxisomal beta-oxidation system, however, the reported biochemical aberrations can no longer be explained by a deficiency of this thiolase. In this study, we show that the true defect in this patient is at the level of d-bifunctional protein (DBP). Immunoblot analysis revealed the absence of DBP in postmortem brain of the patient, whereas THIO was normally present. In addition, we found that the patient had a homozygous deletion of part of exon 3 and intron 3 of the DBP gene, resulting in skipping of exon 3 at the cDNA level. Our findings imply that the group of single-peroxisomal beta-oxidation-enzyme deficiencies is limited to straight-chain acyl-CoA oxidase, DBP, and alpha-methylacyl-CoA racemase deficiency and that there is no longer evidence for the existence of THIO deficiency as a distinct clinical entity.
Human membrane 17 beta-hydroxysteroid dehydrogenase 2 is an enzyme essential in the conversion of the highly active 17beta-hydroxysteroids into their inactive keto forms in a variety of tissues. 17 beta-hydroxysteroid dehydrogenase 2 with 6 consecutive histidines at its N terminus was expressed in Sf9 insect cells. This recombinant protein retained its biological activity and facilitated the enzyme purification and provided the most suitable form in our studies. Dodecyl-beta-D-maltoside was found to be the best detergent for the solubilization, purification, and reconstitution of this enzyme. The overexpressed integral membrane protein was purified with a high catalytic activity and a purity of more than 90% by nickel-chelated chromatography. For reconstitution, the purified protein was incorporated into dodecyl-beta-D-maltoside-destabilized liposomes prepared from l-alpha-phosphatidylcholine. The detergent was removed by adsorption onto polystyrene beads. The reconstituted enzyme had much higher stability and catalytic activity (2.6 micromol/min/mg of enzyme protein with estradiol) than the detergent-solubilized and purified protein (0.9 micromol/min/mg of enzyme protein with estradiol). The purified and reconstituted protein (with a 2-kDa His tag) was proved to be a homodimer, and its functional molecular mass was calculated to be 90.4 +/- 1.2 kDa based on glycerol gradient analytical ultracentrifugation and chemical cross-linking study. The kinetic studies demonstrated that 17 beta-hydroxysteroid dehydrogenase 2 was an NAD-preferring dehydrogenase with the K(m) of NAD being 110 +/- 10 microM and that of NADP 9600 +/- 100 microM using estradiol as substrate. The kinetic constants using estradiol, testosterone, dihydrotestosterone, and 20 alpha-dihydroprogesterone as substrates were also determined.