Quantum biochemistry characterization of representative conformations of the sex hormone-binding globulin monomer bound to estradiol, dihydrotestosterone and testosterone

The transport of sex steroid hormones in the plasma is largely mediated by sex-hormone binding globulin (SHBG). SHBG is a functional homodimer, meaning it can bind two sex hormones with similar affinities. This binding occurs through a complex allosteric mechanism. This globulin plays a pivotal role in regulating the availability of sex hormones within target tissues and cells. Given the established correlation between SHBG and various pathological disorders, there has been increasing interest in characterizing the interactions between SHBG and hormones as well as in identifying potential inhibitors or modulators of the SHBG function. In this regard, the present study aims to provide novel insights into the binding of SHBG with estradiol (EST), dihydrotestosterone (DHT), and testosterone (TES). To this end, molecular docking, molecular dynamics, and quantum mechanics were employed here. The analysis of representative conformations of the highest and lowest interaction energies revealed a high degree of similarity in the binding sites. The SHBG::TES interaction, for which structural data are lacking, exhibited a high degree of structural and energetic similarity to the SHBG::EST and SHBG::DHT complexes. Quantum mechanics calculations demonstrated the following order of theoretical binding affinity, from the highest to lowest: SHBG::DHT > SHBG::EST > SHBG::TES. Furthermore, SER42, PHE67, MET107, and MET139 exhibited the lowest interaction energies, thereby emphasizing the critical role of these residues in SHBG coupling and steroid hormone transport. The energetic description of these complexes contributes to a deeper understanding of steroid hormone transport and provides new insights for targeting SHBG in drug discovery.