Sigma receptors are a biologically important family of integral membrane receptors that are critical for learning, memory, drug addiction and aging diseases such as Alzheimer's disease. While functional data for these receptors has been reported during the last decades, a structural understanding is completely missing, a common feature for integral membrane proteins (IMP). Most important for this proposal, the sigma-1 receptor primary sequence does not resemble that of any other mammalian protein and thus potentially have a novel IMP fold. Furthermore, sigma- 1 is known to act as a ligand-regulated amplifier of GPCR-mediated calcium signaling, a novel protein function. Therefore, to further enhance our understanding of the sigma-1 receptor, its novel activity and the IMP fold space in general, we need to determine its 3-dimensional structure. This will also allow us to achieve our long-term goal of making the sigma receptor family a well-defined and potent drug target. During the last few years, NMR spectroscopy has become a major experimental tool for structural investigations of IMPs. We will use functional data to guide our structural biology efforts to determine the 3-dimensional structure of the sigma-1 receptor using NMR spectroscopy. We will express, purify, solubilize and determine the structure of the sigma-1 receptor using liquid state NMR spectroscopy. To do this we will carefully characterize the activity of the recombinantly expressed and resolubilized sigma-1 receptor in a variety of detergents. This will enable us to find the optimal micelle for activity and structural studies. Lastly, we will pursue an in-depth pharmacological characterization of sigma- 1 in the identified optimal conditions. The sigma-1 3-dimensional structure will then be used to further the understanding of its critical biological functions. Specifically, we will use NMR spectroscopy and additional biophysical techniques to screen a small tailored library of structurally and functionally diverse sigma-1 receptor ligands, both agonists and antagonists, to identify sigma-1 residues and domains responsible for binding. This will enable us to categorize distinct agonist and antagonist binding sites on the sigma-1 receptor. Together, this work will form the foundation of our goal to make the sigma receptor family a comprehensively characterized drug target, critical for finding cures for drug addiction and a variety of aging diseases.
Sigma-1 receptors are potent enhancers of cell signaling and directly linked with diseases such as drug addiction, cancer and Alzheimer's disease. Only by providing a 3-dimensional model of this protein structure based drug design can be successfully employed, a technique which has been a success story for AIDS, flu, glaucoma and arthritis. Therefore, this research plan needs to be executed in a timely manner to establish the sigma receptor family as a well-characterized drug target.