Castration-resistant prostate cancer is the lethal condition suffered by prostate cancer patients that become refractory to androgen deprivation therapy. EPI-001 is a recently identified compound active against this condition that modulates the activity of the androgen receptor, a nuclear receptor that is essential for disease progression. The mechanism by which this compound exerts its inhibitory activity is however not yet fully understood. Here we show, by using high resolution solution nuclear magnetic resonance spectroscopy, that EPI-001 selectively interacts with a partially folded region of the transactivation domain of the androgen receptor, known as transactivation unit 5, that is key for the ability of prostate cells to proliferate in the absence of androgens, a distinctive feature of castration-resistant prostate cancer. Our results can contribute to the development of more potent and less toxic novel androgen receptor antagonists for treating this disease.

component of the cytoplasmic dynein biological motor complex has a relatively large number of interacting partners and fits the description of a hub. Partner proteins of LC8 include the intermediate chain (IC) subunit of cytoplasmic dynein, Chica, a mitotic spindle-associated protein, Nup159, a component of the yeast nuclear pore complex, and a wide array of proteins with roles in apoptosis, enzyme regulation and viral pathogenesis. Linear motifs mediate binding between LC8 and its partner proteins, but while partner proteins such as dynein IC have only one recognition motif, others such as Chica and Nup159 are enriched with multiple interacting motifs. To better understand the importance of multiple recognition motifs in the LC8 interaction network, we have initiated structural and thermodynamic studies of the LC8/Chica and LC8/Nup159 complexes. Chica and Nup159 have four and six putative recognition motifs respectively, nestled within segments that are intrinsically disordered. Our results indicate that LC8 forms a dynamic complex with both proteins, binding only three (Chica) or five (Nup159) of the putative recognition motifs. Furthermore, we show that only three LC8 dimers are needed for optimal stability of the Nup159/LC8 complex, and suggest that the evolutionary adaptation of multiple LC8 recognition motifs imparts to the complex other properties such as rigidity. These findings extend the repertoire of functions of intrinsically disordered proteins to fine-tuning and versatile assembly of higher order macromolecular complexes. 3475-Pos Board B203Conformational Allostery in Nuclear Receptor/Coregulator Transcriptional Complexes By recruiting chromatin remodeling machinery to promoter regions of target genes, nuclear receptors (NRs) act as ligand-dependent transcriptional protein scaffolds, exerting powerful influences on all aspects of physiology. The critical mediators that bridge NRs to the transcriptional machinery are called NR coregulators. NR coregulators are broadly classified into coactivators or corepressors depending on their ability to promote or repress gene transcription. Coactivators contain a cluster of "LXXLL" motifs in a flexible/disordered region called the Receptor Interaction Domain (RID) that mediates their interactions with NRs. Because there is very little atomic level structural information on disordered coactivator RIDs, the physical mechanism driving the interaction between coregulator RIDs and NR transcriptional complexes is poorly understood. We are studying the interaction of Steroid Receptor Coactivator-2 (SRC-2) with the PPARg-RXR transcriptional complex as a model system for understanding NR/coregulator interactions on the atomic level. SRC-2 is a critical coactivator in the PPARg-driven differentiation of mesenchymal stem cells into fat cells, a pathway that is a target for therapeutic intervention of metabolic syndrome and type 2 diabetes. Using biochemical, biophysical and solution NMR approaches, we have begun to probe the interaction of the SRC-2 RID with the full-leng...