Structural Insights into Calcium Signaling at ER-Mitochondria Contact Sites

Mitochondria are essential organelles that play a central role in energy production, metabolic processes, and cellular signaling. Dysfunction in mitochondria is linked to various diseases, including metabolic disorders, neurodegenerative diseases, and cancer. ER-mitochondria contact sites (EMCs) are critical for mitochondrial regulation, facilitating calcium transfer necessary for ATP production. Imbalances in this process can trigger cell death or autophagy, making EMCs key to cell survival and disease progression. Our research delves into the molecular intricacies of EMCs, focusing on the inositol 1,4,5-trisphosphate receptors (IP3Rs) and ER-mitochondria tethering complexes, which are fundamental to calcium signaling and organelle connectivity. We employ advanced structural techniques like X-ray crystallography and cryo-electron microscopy (cryo-EM), combined with biochemical and functional assays, to unravel the mechanisms governing IP3R-mediated calcium release and the formation of tethering complexes that regulate the physical interface between the ER and mitochondria. In addition to their roles in mitochondrial calcium uptake, IP3Rs play extensive roles in cellular signaling pathways. Our research aims to understand the activation, inhibition, and regulation of IP3Rs, which are potential targets for therapeutic intervention in various pathologies. Additionally, we examine the dynamic interactions of tethering complexes, specifically between PTPIP51 and VAPB proteins, to discern the structural features that control EMC assembly and disassembly, which are critical for mitochondrial function and apoptosis. We are developing an in vitro reconstitution system to mimic the membrane interface of EMCs, allowing us to dissect the complex nature of these organelle contacts. Through this system, we will explore how specific mutations and posttranslational modifications influence complex formation and mitochondrial calcium uptake, providing insights into the physiological and pathological roles of these interactions. Our comprehensive characterization of IP3Rs and tethering complexes aims to offer broad insights into cellular physiology, with the potential to significantly advance biomedical research. By elucidating the regulation of mitochondrial calcium influx and its implications for cellular function and disease, we aim to enhance our understanding of intracellular signaling, metabolic regulation, and stress responses. The outcomes of our research hold promise to enhance our fundamental understanding of biology and inform the development of new therapeutic strategies. Project Number: 1R35GM161399-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of General Medical Sciences (NIGMS) | Principal Investigator: ERKAN KARAKAS | Institution: VANDERBILT UNIVERSITY, Nashville, TN | Award Amount: $435,875 | Activity Code: R35 | Study Section: Maximizing Investigators' Research Award B Study Section[MRAB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11259988