Testosterone holds significant medical and economic importance, with the global market for testosterone replacement therapies valued at approximately $1.9 billion in 2023. This hormone is essential for the development and maintenance of male sexual characteristics as well as bone and muscle health. It plays a key role in conditions such as hypogonadism, muscle disorders, and andropause. However, the industrial production of testosterone often involves complex chemical processes that result in low yields, high costs, and environmental damage. Microbial biotransformation of steroids presents an eco-friendly alternative to traditional chemical synthesis. A knockout strain of Aspergillus nidulans deficient in steroid 11-α-hydroxylase activity was developed, rendering it incapable of hydroxylating androstenedione, progesterone, and testosterone. In this strain, two newly identified CYP450 enzymes—CYP68L1 from A. nidulans and CYP68L8 from Aspergillus ochraceus—were expressed to confirm their roles as steroid 11-α-hydroxylases. These enzymes successfully hydroxylated steroids such as androstenedione, progesterone, and testosterone. The availability of these 11-α-hydroxylases represents significant progress toward achieving efficient single-step steroid fermentation. Furthermore, the A. nidulans knockout strain is proposed as an effective model for studying the conversion of androstenedione to testosterone owing to its inability to hydroxylate the testosterone produced during bioconversion.

7α- and 7β-hydroxysteroid dehydrogenases (HSDH) are a pair of enzymes that can catalyze the isomerization of hydroxyl group at site 7 of bile acids. In previous study, we found that the activities of 7α- and 7β-HSDH can be inhibited by bilirubin. In order to clarify the impact, the effects of bilirubin on enzymes were studied by kinetics, spectrum and docking analysis. Relative activity of 7α-HSDH remained less than 40 % under 1 mM bilirubin, for 7β-HSDH, only 18 % activity left at the same condition. Using taurochenodeoxycholic acid (TCDCA) as substrate, the Km of 7α-HSDH was up to 0.63 mM from 0.24 mM after binding with bilirubin, the Km of 7β-HSDH rose from 1.14 mM to 1.87 mM for the catalysis of tauroursodeoxycholic acid (TUDCA). The affinity of 7α- and 7β-HSDH to substrate decreased with the effect of bilirubin. The binding of bilirubin with 7α- or 7β-HSDH were analyzed by UV–Vis spectra, Fluorescence spectra and Circular dichroism (CD) spectra. The results reflected that bilirubin caused a slight change in the secondary structure of 7α- or 7β-HSDH, and the changes were correlated with the ratio of bilirubin to enzyme. 10 candidate molecular docking results were presented to reflect the binding of bilirubin with 7α- or 7β-HSDH and to explore the inhibition mechanism. This research not only provides the more in-depth understanding of 7α- and 7β-HSDH, but also reminds us to avoid the inhibition of bilirubin on hydroxysteroid dehydrogenases.

The biosynthesis of C27-29 sterols from their C30 precursor squalene involves C24-alkylation and removal of three methyl groups, including two at the C4 position. The two C4 demethylation reactions require a bifunctional enzyme known as 3β-hydroxysteroid dehydrogenase/C4-decarboxylase (3βHSD/D) that removes an oxidized methyl (carboxylic) group at C4 while simultaneously catalyzing the 3β-hydroxyl3-keto oxidation. Its loss-of-function mutations cause ergosterol-dependent growth in yeast and congenital hemidysplasia with ichthyosiform erythroderma and limb defect (CHILD) syndrome in humans. Although plant 3βHSD/D enzymes were well studied enzymatically, their developmental functions remain unknown. Here we employed a CRISPR/Cas9-based genome-editing approach to generate knockout mutants for two Arabidopsis 3βHSD/D genes, HSD1 and HSD2, and discovered the male gametophytic lethality for the hsd1 hsd2 double mutation. Pollen-specific expression of HSD2 in the heterozygous hsd1 hsd2/+ mutant not only rescued the pollen lethality but also revealed critical roles of the two HSD genes in embryogenesis. Our study thus demonstrated essential functions of the two Arabidopsis 3βHSD/D genes in male gametogenesis and embryogenesis.