Formation of a Chloride-conducting State in the Maltose ATP-binding Cassette (ABC) Transporter.

ATP-binding cassette transporters use an alternating access mechanism to move substrates across cellular membranes. This mode of transport ensures the selective passage of molecules while preserving membrane impermeability. The crystal structures of MalFGK2, inward- and outward-facing, show that the transporter is sealed against ions and small molecules. It has yet to be determined whether membrane impermeability is maintained when MalFGK2 cycles between these two conformations. Through the use of a mutant that resides in intermediate conformations close to the transition state, we demonstrate that not only is chloride conductance occurring, but also to a degree large enough to compromise cell viability. Introduction of mutations in the periplasmic gate lead to the formation of a channel that is quasi-permanently open. MalFGK2 must therefore stay away from these ion-conducting conformations to preserve the membrane barrier; otherwise, a few mutations that increase access to the ion-conducting states are enough to convert an ATP-binding cassette transporter into a channel.

Selectively targeting the dimerization interface of human androgen receptor with small-molecules to treat castration-resistant prostate cancer.

Prostate cancer (PCa) is a leading cause of death for men in North America. The androgen receptor (AR) - a hormone inducible transcription factor - drives expression of tumor promoting genes and represents an important therapeutic target in PCa. The AR is activated by steroid recruitment to its ligand binding domain (LBD), followed by receptor nuclear translocation and dimerization via the DNA binding domain (DBD). Clinically used small molecules interfere with steroid recruitment and prevent AR-driven tumor growth, but are rendered ineffective by emergence of LBD mutations or expression of constitutively active variants, such as ARV7, that lack the LBD. Both drug-resistance mechanisms confound treatment of this 'castration resistant' stage of PCa (CRPC), characterized by return of AR signalling. Here, we employ computer-aided drug-design to develop small molecules that block the AR-DBD dimerization interface, an attractive target given its role in AR activation and independence from the LBD. Virtual screening on the AR-DBD structure led to development of prototypical compounds that block AR dimerization, inhibiting AR-transcriptional activity through a LBD-independent mechanism. Such inhibitors may potentially circumvent AR-dependent resistance mechanisms and directly target CRPC tumor growth.