TMEM65 functions as the mitochondrial Na⁺/Ca²⁺ exchanger

Area of Science:

• Mitochondrial biology
• Ion transport
• Cellular signaling

Background:

• Mitochondria regulate intracellular calcium (Ca2+) via Na+/Ca2+ exchange (mito-NCX).
• The protein TMEM65 was suggested to be essential for mito-NCX, but its function was unclear.
• Mitochondrial Ca2+ homeostasis is crucial for cellular function and disease pathogenesis.

Purpose of the Study:

• To elucidate the role and mechanism of TMEM65 in mitochondrial Na+/Ca2+ exchange.
• To establish TMEM65 as the functional protein mediating mito-NCX.
• To identify TMEM65 as a potential therapeutic target for mitochondrial Ca2+ dysregulation.

Main Methods:

• TMEM65 depletion studies in cells.
• Biochemical analyses of TMEM65 protein structure and function.
• Heterologous expression of TMEM65 and liposome reconstitution assays.
• Characterization of TMEM65 interaction with the inhibitor CGP-37157.

Main Results:

• TMEM65 depletion significantly impairs mito-NCX activity.
• TMEM65 forms a functional homodimer with ion-coordinating residues.
• TMEM65 expression confers Na+/Ca2+ exchange activity in heterologous systems.
• Purified TMEM65 reconstituted in liposomes exhibits mito-NCX properties.
• The binding site for the inhibitor CGP-37157 was identified.
• TMEM65 deletion leads to elevated mitochondrial Ca2+ and increased mitochondrial permeability.

Conclusions:

• TMEM65 is definitively identified as the protein responsible for mitochondrial Na+/Ca2+ exchange (mito-NCX).
• TMEM65 function is critical for maintaining mitochondrial Ca2+ homeostasis.
• TMEM65 represents a novel therapeutic target for conditions involving aberrant mitochondrial Ca2+ signaling.