2.A.136. The Mitochondrial TMEM65 Na⁺/Ca²⁺ Exchanger (TMEM65-NCX) Family Tmem65 plays a role in cardiac development and function and may regulate cardiac conduction as well as the function of the gap junction protein GJA1 (TC# 1.A.24.1.1). It may also contribute to the stability and proper localization of GJA1 in the cardiac intercalated disk, thereby regulating gap junction communication. It may also regulate mitochondrial respiration and mitochondrial DNA copy number maintenance (Nazli et al. 2017). It is critical for the structure and function of the intercalated discs in mouse hearts (Teng et al. 2022). This family was previously TC family 8.A.205 before its ion exchange function was reported (Zhang et al. 2025). Mitochondria export Ca²⁺ via Na⁺/Ca²⁺ exchange (mito-NCX) to regulate intracellular Ca²⁺ signalling and mitochondrial Ca²⁺ homeostasis. TMEM65 has been implicated as essential for mito-NCX (Zhang et al. 2025). TMEM65 depletion severely impaired mito-NCX. This protein is highly expressed in the heart and brain but absent in the liver, correlating with mito-NCX activity in these tissues. Biochemical and functional analyses reveal that TMEM65 forms a homodimer, containing plausible ion-coordinating residues critical for function. Heterologous expression of TMEM65 induces Na⁺/Ca²⁺ exchange in cells lacking native mito-NCX activity. Moreover, purified, liposome-reconstituted TMEM65 exhibited key mito-NCX features. Zhang et al. 2025 also identify the binding site for CGP-37157, a potent, widely used mito-NCX inhibitor. Finally, TMEM65 deletion elevated mitochondrial Ca²⁺ and primed mitochondria for the permeability transition. These findings establish TMEM65 as the protein mediating mito-NCX, offering a new therapeutic target for diseases associated with mitochondrial Ca²⁺ dysregulation.
References:
Nazli, A., A. Safdar, A. Saleem, M. Akhtar, L.I. Brady, J. Schwartzentruber, and M.A. Tarnopolsky. (2017). A mutation in the TMEM65 gene results in mitochondrial myopathy with severe neurological manifestations. Eur J Hum Genet 25: 744-751.
Teng, A.C.T., L. Gu, M. Di Paola, R. Lakin, Z.J. Williams, A. Au, W. Chen, N.I. Callaghan, F.H. Zadeh, Y.Q. Zhou, M. Fatah, D. Chatterjee, L.J. Jourdan, J. Liu, C.A. Simmons, T. Kislinger, C.M. Yip, P.H. Backx, R.G. Gourdie, R.M. Hamilton, and A.O. Gramolini. (2022). Tmem65 is critical for the structure and function of the intercalated discs in mouse hearts. Nat Commun 13: 6166.
Zhang, J.L., Y.C. Chang, P.H. Lai, H.I. Yeh, C.W. Tsai, Y.L. Huang, T.Y. Liu, I.C. Lee, N. Foulon, Y. Xu, B. Rao, H.M. Shih, Y.C. Tu, A.V. Reyes, S.L. Xu, L. Feng, and M.F. Tsai. (2025). TMEM65 functions as the mitochondrial Na/Ca exchanger. Nat. Cell Biol. 27: 1301-1310.