Mangelsdorf, David J.2011-09-302014-02-192012-12-012014-02-192010-01-12761318098http://hdl.handle.net/2152.5/919Bile acids are not only detergents for lipid solubilization and absorption, but also important signaling molecules. They regulate biological events in mammals by acting on nuclear receptors and membrane-bound receptors. Bile acid homeostasis is maintained in part through a FXR-SHP signaling circuit, in which SHP functions as a transcriptional corepressor. The mechanism whereby SHP represses was one focus of my thesis research. I used a number of biochemical strategies including tandem affinity purification to identify SHP interacting proteins. I also successfully solubilized SHP recombinant protein, which was used to generate crystals that diffracted to 3.2 Angstroms. Bile acid-like molecules function in nematodes to control a variety of life history traits such as dauer and infective L3 formation through the nuclear receptor DAF-12. Although DAF-12 homologues from different nematode species are functionally and structurally conserved, they show differential pharmacological responses to ligands. To that end, I solved the X-ray crystal structure of the hookworm Ancylostoma ceylanicum DAF-12 ligand binding domain and revealed the molecular basis underlying species specific-ligand binding for DAF-12. Furthermore, DAF-12 was shown to be structurally similar to the bile acid sensor FXR, suggesting bile acid-like signaling pathways have been conserved across evolution. In conclusion, my studies provide new insights into how bile acids are sensed and regulated in mammals and nematodes. [Keywords: bile acids; SHP; FXR; DAF-12; Dafachronic acids; hookworm; protein expression; crystallization]enBile Acids and SaltsReceptors, Cytoplasmic and NuclearHomeostasisThesis