Topological characterization of the mitochondrial phospholipid scramblase 3

Scramblases redistribute phospholipids in biological membranes. Phospholipid scramblase 3 (PLSCR3), which is located in mitochondria, has been reported to be involved in cardiolipin distribution from the inner to the outer membrane, thus regulating cellular processes such as apoptosis or mitophagy. However, the localization and topology of this protein has not been convincingly addressed to support a role in intermembrane phospholipid transfer. Here, we studied PLSCR3 topology within mitochondria. We show that PLSCR3 inserts in the inner membrane (IM) via its C‐terminal transmembrane helix, whereas its N‐terminal portion is oriented toward the intermembrane space where it is activated by calcium. Our results suggest that PLSCR3, via its C‐terminal transmembrane domain, participates in the bidirectional movement of phospholipids within the IM.