Fine-Tuning the Processes of Steroid Hormone Biosynthesis: SULT2A1/1E1 and CYP21A2 Interaction

The high physiological activity of steroid hormones requires multilevel regulation of their biosynthesis. Cytosolic sulfotransferases, specifically SULT2A1 and SULT1E1, convert steroid precursors into mobile sulfated depot forms, diverting them from key steroidogenic cytochromes P450. Given the previously demonstrated CYP17A1–SULT interactions, this study aims to verify the hypothesis that CYP21A2 can interact with SULTs and thereby potentially contribute to the regulation of steroid metabolism. Using surface plasmon resonance (SPR) biosensing, in vitro enzymatic activity assays, and in silico molecular modeling, we investigated the interplay between CYP21A2 and SULT2A1/1E1. SPR analysis revealed high-affinity binding between purified recombinant CYP21A2 and SULT2A1/SULT1E1 in vitro in the nanomolar range (9.5 × 10−9 M for SULT2A1 and 1.15 × 10−8 M for SULT1E1). Thermodynamic assessments indicated that the CYP21A2–SULT1E1 complex is entropy-driven, contrasting with the enthalpy-driven CYP17A1–SULT1E1 interaction. Enzymatic assays demonstrated reciprocal modulatory effects: CYP21A2 exerted a stimulatory effect on pregnenolone sulfation by SULTs, whereas SULT2A1 moderately inhibited CYP21A2 activity. Molecular modeling of binary complexes predicted structural interfaces and continuous intraprotein channels connecting the enzymes’ active sites. These findings suggest that CYP–SULT interactions may contribute to the fine-tuning of steroid hormone biosynthesis. These findings raise the possibility that CYP–SULT interactions may form part of a broader regulatory network, acting as metabolic switches that dictate the balance between downstream corticosteroid pathways and structural sequestration into sulfated pools.