Researchers report that a group of proteins known as MICUs act as molecular organizers, assembling energy-generating machinery in response to calcium signals—without relying on calcium entering the interior mitochondrial matrix.
For nearly half a century, biology textbooks have taught a simple idea: calcium ions power up the cell’s energy factories by flowing into mitochondria. But a new study is challenging that long-standing assumption—and revealing a previously hidden system that may be the true conductor of cellular energy production.
Researchers at Temple University’s Lewis Katz School of Medicine report that a group of proteins known as MICUs act as molecular organizers, assembling energy-generating machinery in response to calcium signals—without relying on calcium entering the interior mitochondrial matrix. The discovery reshapes scientific understanding of how cells match energy production with demand and could have far-reaching implications for diseases ranging from heart failure to cancer to neurodegeneration.
The study was published online May 13, 2026 in the journal Nature Metabolism.
“This work changes the way we think about how calcium regulates metabolism at a fundamental level,” said John W. Elrod, PhD, Director of the Aging + Cardiovascular Discovery Center (ACDC) and W.W. Smith Chair of Cardiovascular Medicine at Temple University’s Lewis Katz School of Medicine, and senior investigator on the new study. “Instead of calcium acting inside mitochondria, we’re seeing that it can control energy production from the outside (within the inner membrane space) by influencing the organization of a metabolic enzyme complex within the mitochondrial matrix.”
Mitochondria produce the energy that keeps cells alive, and calcium has long been thought to regulate this process by entering the mitochondrial matrix and activating key enzymes. Yet for years, experimental results have not fully supported this model. Even when scientists disabled the main gateway for calcium entry—the mitochondrial calcium uniporter—cells often continued producing energy normally under baseline conditions.
“This disconnect posed a fundamental question: if calcium entry isn’t essential, how does calcium actually regulate metabolism?” Dr. Elrod said.
To answer this question, the researchers, led by Henry M. Cohen, an MD, PhD graduate student in Dr. Elrod’s laboratory, used CRISPR-based gene editing technology to genetically modify cells to either delete or express specific mitochondrial proteins. This strategy allowed them to isolate the roles of individual MICU proteins.
They also created specialized models with tagged versions of these proteins to track their behavior in living systems via high-resolution imaging techniques developed by collaborator Wolfgang F. Grair, PhD, at Gottfried Schatz Research Center at the Medical University of Graz in Austria. Using imaging, alongside immunoprecipitation and mass spectrometry, the team mapped the interaction networks—or “interactomes”—formed by different MICU protein combinations.
These experiments revealed that distinct combinations of MICU proteins assemble unique sets of metabolic partners, forming complexes known as metabolons. Functional assays showed that metabolons directly influence mitochondrial function. For example, the researchers demonstrated that MICU2 enhances the activity of a metabolic module linking glycerol-3-phosphate dehydrogenase and Complex II, a crucial enzyme that bridges essential processes in metabolism.
Additional experiments measuring mitochondrial metabolism confirmed that these protein assemblies regulate energy production independently of calcium uptake into the mitochondrial matrix. By coordinating these pathways at a central junction, the inner membrane space, MICU proteins help balance energy production, redox state, and cellular demand—functions that are critical in tissues with high energy needs, such as the heart and brain.
“These metabolons that are formed in response to calcium signaling physically link key energy-producing enzymes allowing them to work together more efficiently,” Dr. Elrod explained. “Metabolons are organized complexes of metabolic enzymes. The result is a system that dynamically adjusts energy production to match the cell’s needs, without requiring changes in internal mitochondrial calcium levels.”
This represents a major conceptual shift. The researchers propose that MICU-driven metabolon formation—not calcium entry into the mitochondrial matrix—is the primary physiological mechanism by which calcium regulates energy production under normal conditions. The work is also the first to demonstrate that MICU proteins can directly organize metabolic machinery in response to calcium signaling independent of the mitochondrial calcium uniporter.
“By identifying these metabolons, we’ve uncovered an entirely new layer of metabolic regulation,” added Dr. Elrod. “It opens the door to targeting metabolism in a more systematic way than we could before.”
The researchers next plan to focus on understanding how this system operates in living organisms under stress conditions, such as exercise, aging, or disease. They also aim to explore whether disruptions in MICU-mediated metabolon formation contribute to metabolic disorders—and whether targeting these protein interactions could offer new therapeutic opportunities.
Other researchers involved in the study include: Carmen Choya-Foces, Adam Chatoff, Anya
Wilkinson, Elena Berezhnaya, Joanne F. Garbincius, Adyson Johnson, Tyler L. Stevens, Jordan E. Howe, Hailey Lesniak, Anna Schmidt, Jennyfer Ngo, Emily Megill, Dhanendra Tomar, and Nathaniel W. Snyder, Aging + Cardiovascular Discovery Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine; and Benjamin Gottschalk, Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Austria.
The study was funded in part by grants from the National Institutes of Health and the American Heart Association.