Daniel M. Rosenbaum
Biophysical Characterization of Conformational Changes in Disease-related Membrane Proteins
Membrane proteins are the key points of contact between the intracellular and extracellular environments, allowing the flow of molecules and information into and out of the cell. Integral membrane proteins are also involved in a variety of intracellular signaling and regulatory processes, a notable example being the maintenance of sterol homeostasis. While structural approaches have had an enormous impact on our understanding of the functions of soluble proteins, the molecular mechanisms of many physiologically important and disease-related membrane proteins remains opaque. To address this challenge, we have helped to develop new techniques that have already made a significant impact in the study of G protein-coupled receptors (GPCRs). One of these developments is the use of protein engineering to make membrane proteins more amenable to crystallization and structure determination. Another essential development is the advent of lipid-mediated crystallization methods that allow us to preserve and visualize membrane protein structure in a more native lipid-containing environment. The powerful combination of these tools has led to over 10 GPCR crystal structures in the past five years, revealing unprecedented molecular details about these ubiquitous hormone receptors.
We are employing these tools to gain a deeper understanding of the SREBP pathway, which is a primary mechanism used by the cell to maintain tight control over membrane lipid composition. Little is known at a biophysical level about the membrane proteins involved, including Scap and Insig, which respond to sterol levels in the endoplasmic reticulum membrane and control the activation of SREBP transcription factors. Our aims are to solve three-dimensional crystal structures of these membrane proteins alone and in functionally relevant complexes, and to use fluorescence techniques to probe conformational changes in response to different lipids. Since the SREBP pathway is involved in the pathogenesis of metabolic and cardiovascular diseases, molecular insights may open the door to development of new therapeutics.