Binding of Steroid Hormones to the FA1 and FA6 Sites of Human Serum Albumin through Computational Biology and Quantum Biochemistry

Human serum albumin (HSA) plays a significant role in the transportation of steroid hormones through noncovalent interactions of low affinity. The binding between HSA and estradiol and testosterone has been a subject of investigation through experimental tools. While some studies suggest that HSA carries sex steroid hormones through a unique binding site, others propose that this interaction occurs through two or three binding sites, indicating a lack of consensus regarding the mechanisms underlying these interactions. In view of this, the present study used molecular docking, molecular dynamics, and quantum biochemistry to obtain more insights into the binding of estradiol, dihydrotestosterone, and testosterone to HSA. Molecular docking indicated that fatty acid binding sites 1 (FA1) and 6 (FA6), located respectively in subdomain IB and between subdomains IIA and IIB, are particularly promising targets for more robust investigations. The hormones exhibited considerable flexibility within subdomain IB, with dihydrotestosterone showing the greatest structural stability. This hormone also demonstrated the highest stability within FA6, which was markedly greater than that observed at FA1. Quantum mechanics calculations suggested that the three hormones exhibit similar interaction energies for the FA1 binding site, with estradiol predicting a marginally lower energy of interaction. Dihydrotestosterone was the only hormone that exhibited both the highest structural stability and the lowest energy of interaction when bound to FA6. Overall, the results suggest that the FA1 and FA6 binding sites generally do not favor the formation of strong interactions, except in the HSA-FA6:Dihydrotestosterone complex, where the hydrogen bond LEU481(HN-main chain):DHT(O17) played a crucial role in stabilizing conformations of both high and low theoretical energy of interaction. This observation aligns with the established fact that the interaction between HSA and sex steroid hormones is weak. Moreover, the present study found that dihydrotestosterone exhibits a heightened tendency to bind to FA6 in comparison to estradiol and testosterone. This tendency may critically regulate DHT serum transport, bioavailability, and half-life, while also creating a pharmacologically relevant hotspot for competition with fatty acids and FA6-targeting drugs, with potential implications for hormonal homeostasis and drug-hormone interactions in physiological and pathological conditions.