Glutathione Transferases as Efficient Ketosteroid Isomerases

Abstract

In addition to their well-established role in detoxication, glutathione transferases (GSTs) have other biological functions. We are focusing on the ketosteroid isomerase activity, which appears to contribute to steroid hormone biosynthesis in mammalian tissues. A highly efficient GST A3-3 is present in some, but not all, mammals. The alpha class enzyme GST A3-3 in humans and the horse shows the highest catalytic efficiency with kcat/Km values of approximately 107 M−1s−1, ranking close to the most active enzymes known. The expression of GST A3-3 in steroidogenic tissues suggests that the enzyme has evolved to support the activity of 3β-hydroxysteroid dehydrogenase, which catalyzes the formation of 5-androsten-3,17-dione and 5-pregnen-3,20-dione that are substrates for the double-bond isomerization catalyzed by GST A3-3. The dehydrogenase also catalyzes the isomerization, but its kcat of approximately 1 s−1 is 200-fold lower than the kcat values of human and equine GST A3-3. Inhibition of GST A3-3 in progesterone-producing human cells suppress the formation of the hormone. Glutathione serves as a coenzyme contributing a thiolate as a base in the isomerase mechanism, which also involves the active-site Tyr9 and Arg15. These conserved residues are necessary but not sufficient for the ketosteroid isomerase activity. A proper assortment of H-site residues is crucial to efficient catalysis by forming the cavity binding the hydrophobic substrate. It remains to elucidate why some mammals, such as rats and mice, lack GSTs with the prominent ketosteroid isomerase activity found in certain other species. Remarkably, the fruit fly Drosophila melanogaster, expresses a GSTE14 with notable steroid isomerase activity, even though Ser14 has evolved as the active-site residue corresponding to Tyr9 in the mammalian alpha class.

Potent GST ketosteroid isomerase activity relevant to ecdysteroidogenesis in the malaria vectorAnopheles gambiae

“…Our proposed mechanism for Nobo in the steroid double-bond isomerization is similar to the bacterial ketosteroid isomerase reaction by invoking a carboxylate, which polarizes C=O in position C3 of the steroid substrate (Yabukarski et al 2022). Like in the mammalian GSTs with steroid isomerase activity (Mannervik et al 2021), the glutathione thiolate in Nobo serves as the base attacking the C4 hydrogen. In other respects the enzymes differ in functional groups even though they catalyze the same reaction.…”

The role of proteins implicated in skin steroidogenesis in acne vulgaris development

“…Выделяют два типа данного фермента. Активность 3βHSD типа I была обнаружена в плаценте, молочных железах, печени, головном мозге, коже и некоторых других органах, тогда как 3βHSD типа II присутствует только в надпочечниках и гонадах [12]…”

Myricetin as a Potential Adjuvant in Chemotherapy: Studies on the Inhibition of Human Glutathione Transferase A1–1

“…Glutathione transferases (GSTs) are multifunctional enzymes that have evolved from thioredoxins/glutaredoxins family [ 1 , 2 , 3 , 4 ]. They contribute to biotic/abiotic stress responses by eliminating reactive electrophile species [ 1 , 2 , 5 , 6 , 7 , 8 ].…”

“…Glutathione transferases (GSTs) are multifunctional enzymes that have evolved from thioredoxins/glutaredoxins family [ 1 , 2 , 3 , 4 ]. They contribute to biotic/abiotic stress responses by eliminating reactive electrophile species [ 1 , 2 , 5 , 6 , 7 , 8 ]. The human GST gene family comprises sixteen genes that are grouped in six subfamilies: alpha (GSTA), mu (GSTM), omega (GSTO), pi (GSTP), theta (GSTT), and zeta (GSTZ) [ 9 , 10 ].…”