Biochemical Characteristics And Physiological Function Exploration Of STIM1Molecule

The calcium signals control a broad spectrum of the cell physiological functions ranging from contraction, secretion to transcription, proliferation and apoptosis. Different pumps and versatile channels in the cell are the basis for generation of calcium signals. In non-exciting cells, extracellular calcium enters the cell across the PM mainly through the Store Operated Calcium channels which is activated while the calcium store is depleted. After extensive study, the Orail is indentified as the pore forming units in the plasma membrane while the Stromal Interaction Molecule1(STIM1) is the calcium sensor mainly located on the ER membrane. These two proteins are reported to be crucial for SOCE.With the development of single cell technology and the application of electrophysiological techniques, much is known about the interaction area of STIM1and Orail. Especially the structure of STIM1N terminal solved by NMR method helps us to understand how STIM1senses the calcium change in the ER. But nothing is known about the structure of the large C terminal. Therefore the detailed information about the interaction mechanism of STIM1and Orail is still unknown. Here we systematically expressed the C terminal region of STIM1and screening the crystals. At last, we got the pure protein and crystals of the SOAR (STIM1, Orai1activating region) domain of STIM1.From the SOAR atomic structure along with other results from our lab, we propose a model for STIM1activation:In the resting state, STIM1mainly exists as a dimer, and the activating region is hidden in the large C terminal and inhibited by an Inhibitory helix (IH). During activation, the disassociation of calcium from the EF-SAM triggers the conformational change and cause elongation of the C terminal to release the SOAR region. Then the STIM1aggregates and activates Orail channels on the PM.Further,we tried to explore the role of STIM1and Orail in cardiac hypertrophy. Results showed that the silencing of STIM1and orail by corresponding SiRNA can neutralize the hypertrophic phenotype of cardiomyocytes caused by pathological signals. We also found there is a cross talk between the STIM1/Orail and the PKD3pathways.Taken together, our results provide important structural infomation on the menchnism of STIM1activation. This is also significant for studying the regulation of SOCE process. The next step, we may mainly focused on the gating and turn-off menchnism of the Orail channel. Moreover, searching for the possible role of Stiml, Orai1in cardiac hypertrophy helping us to better undrstand the hypertrophic signaling pathways. However, for the discovery of new therapeutic targets, further works are still needed to be done to specify the pathways STIM1involved in.