Scientists crack the "off switch" for a key brain cell membrane protein

Researchers from Institute of Science Tokyo have uncovered a critical regulatory mechanism in TMEM63B, a protein that controls how lipids are distributed across cell membranes. Under normal conditions, cells maintain a precise, asymmetric arrangement of lipids — and TMEM63B, a mechanosensitive lipid scramblase, must stay inactive to preserve that balance. The new study, published in the Journal of Biological Chemistry, reveals exactly how that "off switch" works.

The team found that the C-terminal tail of TMEM63B contains an autoinhibitory region that acts like a molecular brake, keeping the protein dormant when the membrane is at rest. A single amino acid — Leucine at position 776 (Leu776) — is the linchpin. Mutating it causes the protein to become constitutively active, triggering uncontrolled lipid scrambling even without any membrane stimulus.

Key Takeaways:

• Disrupting Leu776 causes phosphatidylserine (normally confined to the cell's inner membrane) to appear on the outer surface — a hallmark of cellular distress
• TMEM63B mutations have previously been linked to neurodevelopmental and neurodegenerative disorders
• These findings could guide future therapeutic strategies targeting TMEM63B dysregulation

Why it matters: Understanding how TMEM63B is kept in check opens a new window into how its malfunction may drive neurological disease — and could point toward novel drug targets.