| Like the cells they operate, proteins are dynamic, plastic entities. Nowhere in proteins is this more evident than in protein-protein interfaces. In many cases, proteins must be able to recognize not just one partner, but many. The ability to be flexible and accommodating, yet at the same time discriminate against the multitude of unwanted partners in the cell is what allows proteins to make life possible. However, this presents a paradox: how can protein recognition be both specific and promiscuous? In particular, what are the mechanisms that allow broad-specificity in a protein-protein interface, and perhaps more importantly, what insights can this give us toward understanding a protein's biological role in the cell? Answering these questions can potentially lead to new compounds that antagonize protein-protein interfaces and cure disease.; To better understand these issues in the context of the proteolytic blood coagulation cascade, the structure of factor Xa (FXa) was solved in complex with a M84R variant of the macromolecular protease inhibitor ecotin. The structure reveals the atomic mechanism of association. Despite not possessing the recognition sequence of canonical FXa substrates, ecotin binds FXa with pico-molar affinity through a combination of induced fit and nonspecific secondary site interactions.; Toward the aim of developing alternative anti-androgen compounds for prostate cancer, the structure of the androgen receptor (AR) was solved in complex with peptides that mimic the receptors' interactions with coactivators. The complexes reveal both the structural basis of AR's preference for coactivators containing FxxLF motifs, and how AR is able to accommodate motifs containing other hydrophobic residues as well. The structures provide a framework for the design of AR antagonists.; Finally, the AR-NTD and its coregulators represent protein plasticity at its most extreme. Like many transcription factors, they are disordered in the absence of binding partners---folding is induced by association with partner proteins. To understand how the AR N-terminal domain (NTD) interacts with its coregulator partners, a high-throughput coexpression and domain mapping system was developed. This system was used to map the interaction of the orphan receptor LRH-1 and one of its recently discovered coactivators, NCoA-62. |
