Endocrine resistance is one of the most challenging problems in estrogen receptor alpha (ER alpha)-positive breast cancer. The transcriptional activity of ER alpha is controlled by several coregulators, including prohibitin-2 (PHB2). Because of its ability to repress the transcriptional activity of activated ER alpha, PHB2 is a promising antiproliferative agent. In this study, were analyzed the interaction of PHB2 with ER alpha and three mutants (Y537S, D538G, and E380Q) that are frequently associated with a lack of sensitivity to hormonal treatments, to help advance novel drug discovery. PHB2 bound to EIZ alpha wild-type (WT), Y537S, and D538G, but did not bind to E380Q. The binding thermodynamics of Y537S and D538G to PHB2 were favorably altered entropically compared with those of WT to PHB2. Our results show that PHB2 binds to the ligand binding domain of ER alpha with a conformational change in the helix 12 of ER. (C) 2015 Elsevier Inc. All rights reserved.