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Erkan Karakas

Structural Biology of Calcium Signaling and Transport through Biological Membranes

Erkan Karakas, Molecular Physiology & Biophysics

The major goal of the Karakas Lab is understanding the molecular mechanism and regulation of calcium signaling at the endoplasmic reticulum (ER)-mitochondria contact sites, where ER and mitochondria are linked through proteinaceous tethers located at the specialized ER subdomains named as mitochondria-associated membranes (MAMs) and outer membrane of mitochondria. At these sites, inositol 1,4,5-triphosphate (IP3) receptors release calcium from the ER, creating local hot spots necessary for calcium uptake by mitochondrial calcium uniporter (MCU) in the inner mitochondrial membrane. Sustained calcium transfer to mitochondria is necessary to maintain ATP generation, whereas excessive or reduced calcium transfer leads to initiation of apoptotic cell death or autophagy, respectively. Consequently, calcium signaling at ER-mitochondria interface plays an essential role in cell fate decisions and could be an invaluable target when the cell fate decision machinery is compromised, as observed in cancer (evasion of apoptosis) and neurodegenerative diseases (excessive apoptosis).

The overall approach in my laboratory is structural characterization of the target proteins using X-ray crystallography and cryo-EM followed by validation of the structural information and the structure-derived hypotheses. We use a repertoire of biophysical and biochemical methods as well as functional assays to deduce the molecular mechanism of gating, oligomeric assembly, stoichiometry, protein-protein and protein-ligand interactions.

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