An interesting distinction is observed between the vitamin D2 complex and the vitamin D3 complex. In the vitamin D2 complex, residues Asp292 (0.97 kJ/mol) and Lys203 (1.59 kJ/mol) contribute unfavorably to the total binding free energy, while Gln294 plays a significant role. In contrast, the vitamin D3 complex is influenced by Asp204 as a major contributor (Figure ). Both Gln294 and Asp203 form conventional hydrogen bonds with the hydroxyl groups of vitamin D, highlighting their roles in complex stability.