Fellowship for A. Shim in Support of Conformational Dynamics of STIM1 Activation

Store-operated Ca2+ release-activated Ca2+ (CRAC) channels are expressed in many different cell types of the cardiovascular system, including vascular smooth muscle cells (VSMCs), endothelial cells, and platelets. Emerging evidence indicates that the Ca2+ influx through CRAC channels mediates a critical role in the proliferation and migration of these cells, and aberrant channel activity has been linked to cardiovascular diseases, such as restenosis, atherosclerosis, hypertension, and thrombosis. These findings suggest that modulation of CRAC channel activity may be a possible avenue for cardiovascular disease therapy. CRAC channels are made up of two components: the Orai proteins, which form the ion-selective pore, and STIM1 (stromal interacting molecule 1), the ER Ca2+ sensor. It is known that activation of CRAC channels involves coordinated redistributions of the STIM and Orai proteins and bringing them into direct physical contact in the closely juxtaposed membranes of the ER and plasma membrane, respectively. However, the conformational dynamics of STIM1 activation remains poorly understood. In this project, I will employ a powerful combination of mutational analysis, FRET imaging, and protein biophysical techniques to understand the structural and molecular basis of STIM1 activation. Specifically, I will: (1) Delineate the role of dimerization and dimer interface of the minimal catalytic domain called CAD in STIM1 activation, (2) Determine the arrangement of cytosolic coiled-coil domains of a STIM1 protomer in the resting and activated states. Additionally, a loss-of-function human STIM1 mutation and pharmacological modulators will be used as tools to probe conformational changes of STIM1 activation. These studies will illuminate the structural and molecular basis of STIM1 and CRAC channel activation and advance the quest for structure-based drug design efforts targeting CRAC channels for cardiovascular therapeutic applications.