Laura Caboni¹, Debanu Das^2,3, Fumiaki Yumoto^1,4,5, Phuong Nguyen¹,  Elena Sablin¹, Mike Hornsby⁶, Jim Wells⁶, Marc-André Elsliger^2,7, Bruce R. Conklin⁴, Ashley M. Deacon^2,3, Ian A. Wilson^2,7 and Robert J. Fletterick¹

¹Department of Biochemistry and Biophysics, University of California, San Francisco; ²Joint Center for Structural Genomics, http://www.jcsg.org; ³Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park; ⁴Gladstone Institute of Cardiovascular Disease, San Francisco; ⁵Structural Biology Research Center, KEK High Energy Accelerator Research Organization, Oho 1-1, Tsukuba 305-0801,Japan; ⁶Department of Pharmaceutical Chemistry and Cellular & Molecular Pharmacology, University of California, San Francisco; ⁷Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla

The transcription factor Liver Receptor Homolog-1 (LRH-1) is an important nuclear receptor in steroidogenesis, bile acid homeostasis, cholesterol transport and stem cell pluripotency. Much is known about the LRH-1 Ligand Binding Domain (LBD) and the DNA-Binding Domain (DBD), including complexes with co-activators, ligands or DNA, but there is no information on the architecture of the full-length LRH-1, which functions as a monomer. As a result, it is not known how the different domains of the full-length LRH-1 are juxtaposed to each other. In contrast, structures have been determined for some other full-length nuclear receptors, which are homodimeric or heterodimeric. The main hindrance to structural studies of full-length LRH-1 has been the availability of sufficient quantities of stable, soluble protein. We describe the production, purification and stabilization of the full-length LRH-1 in complex with the alpha inhibin promoter; functional characterization by Differential Scanning Fluorimetry (DSF) and Biolayer Interferometry (BLI); and structural characterization by Small Angle X-ray Scattering (SAXS). Additional ternary complexes with antibody fragments designed as targeted molecular tools to study LRH-1 function have been produced and similarly characterized. Our results reveal an extended molecular architecture of the functional LRH-1 that is supported by our SAXS studies on the homologous nuclear receptor, Steroidogenic Factor-1 (SF-1), which lacks an N-terminal domain, in complex with the same DNA duplex. Crystallization trials and preliminary negative stain Electron Microscopy (EM) studies for these complexes are in progress with the ultimate goal of obtaining high resolution crystal or cryoEM structures