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<p>Mitochondrial Ca²⁺ homeostasis is maintained through coordinated influx and efflux processes, with NCLX long recognized as the primary Ca²⁺ extruder operating via Na⁺/Ca²⁺ exchange. Here, we report cryo-EM structures of rat NCLX in cytosolic-facing occluded and open states. The central transmembrane (TM) domain of NCLX comprises ten helices arranged in two inverted, structurally similar halves, with two α-repeats forming a central ion-binding pocket. Peripheral TMs 1 and 6 are loosely associated with the core and likely mediate alternative access to this site. These structural features closely resemble those of NCXs, indicating a conserved ion exchange mechanism. While NCLX retains the canonical Ca²⁺-binding site, it lacks several key Na⁺-binding residues found in NCXs, suggesting broader ion selectivity. Consistently, cell-based Ca²⁺ uptake assays show that NCLX mediates Ca²⁺ exchange using Na⁺, K⁺, Li⁺, and potentially protons as counterions. Based on the structural symmetry of NCLX and its bidirectional exchange capability, we propose a matrix-facing model and an alternating-access mechanism in which TMs 1 and 6 undergo sliding motions to enable ion exchange between cytosolic and matrix sides, analogous to NCX. These findings provide a structural and mechanistic framework for understanding NCLX-mediated Ca²⁺ transport in mitochondria.</p>

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Molecular mechanisms of mitochondrial Ca2+ exchanger NCLX

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月10日

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  • Li Zhang,
  • Yan Han,
  • Weizhong Zeng,
  • Jing Xue,
  • Yan Wang,
  • Youxing Jiang

摘要

Mitochondrial Ca²⁺ homeostasis is maintained through coordinated influx and efflux processes, with NCLX long recognized as the primary Ca²⁺ extruder operating via Na⁺/Ca²⁺ exchange. Here, we report cryo-EM structures of rat NCLX in cytosolic-facing occluded and open states. The central transmembrane (TM) domain of NCLX comprises ten helices arranged in two inverted, structurally similar halves, with two α-repeats forming a central ion-binding pocket. Peripheral TMs 1 and 6 are loosely associated with the core and likely mediate alternative access to this site. These structural features closely resemble those of NCXs, indicating a conserved ion exchange mechanism. While NCLX retains the canonical Ca²⁺-binding site, it lacks several key Na⁺-binding residues found in NCXs, suggesting broader ion selectivity. Consistently, cell-based Ca²⁺ uptake assays show that NCLX mediates Ca²⁺ exchange using Na⁺, K⁺, Li⁺, and potentially protons as counterions. Based on the structural symmetry of NCLX and its bidirectional exchange capability, we propose a matrix-facing model and an alternating-access mechanism in which TMs 1 and 6 undergo sliding motions to enable ion exchange between cytosolic and matrix sides, analogous to NCX. These findings provide a structural and mechanistic framework for understanding NCLX-mediated Ca²⁺ transport in mitochondria.