Integrated structural analysis of sex hormone binding globulin reveals allosteric modulation by distant mutations

Sex hormone-binding globulin (SHBG), a glycoprotein in circulation, binds testosterone, dihydrotestosterone, and estradiol with high specificity, regulating their transport and bioavailability. This function relies on long-range conformational interactions between its N-terminal (NTD) and C-terminal (CTD) domains. Variations in SHBG levels or binding affinities alter free hormone concentrations, influencing reproductive and metabolic health. Despite its significance, the full-length SHBG structure and the conformational dynamics influencing hormone binding remain unclear. Deploying in-silico structural analysis, Raman spectroscopy, and network modeling, we investigated the intramolecular structural dynamics of the full length SHBG to understand how allosteric perturbations caused by natural mutations affect hormone binding and inter-residue interactions. Raman spectroscopy and in-silico analyses show that majority of the residues in SHBG (308 residues) constitute loop regions, whereas only 21 % constitute beta sheet. Mutations in SHBG that alter its binding affinity, though distant from the ligand-binding pocket (LBP), induce long-range conformational changes. These mutations are clustered in flexible regions but maintain structural order through dense local interactions. Our in-silico analyses identified key substructures regulating allosteric interactions between mutation sites and ligand-binding residues. This study provides a template for further structural analyses of clinically reported mutations and their effect on hormone binding and action.