Structural and functional basis of mechanosensitive TMEM63 channelopathies

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• TMEM63A, -B, and -C are mammalian mechanosensitive ion channels implicated in neurodevelopmental disorders.
• The precise mechanisms of TMEM63 channel activation by force and the functional impact of disease mutations remain unclear.

Purpose of the Study:

• To elucidate the structural and functional basis of the TMEM63B p.V44M mutation.
• To investigate the role of disease-associated mutations in TMEM63 channel activity and lipid scrambling.

Main Methods:

• X-ray crystallography was used to solve the structures of TMEM63A p.V53M in closed and lipid-open states.
• Molecular dynamics simulations were employed to study lipid scrambling through the mutant channel.
• Biochemical assays were performed to assess channel activity and lipid scramblase function.

Main Results:

• The TMEM63B p.V44M and TMEM63A p.V53M mutations are gain-of-function, inducing constitutive lipid scramblase activity rather than enhanced channel gating.
• Structural analysis revealed major rearrangements in pore-lining helices, forming a lateral cleft facilitating lipid scrambling.
• Disruption of a hydrophobic latch, a potential force-sensing module containing mutation sites, triggers these structural changes.

Conclusions:

• Disease-associated mutations in TMEM63 channels can lead to constitutive lipid scramblase activity.
• A novel force-sensing mechanism involving a hydrophobic latch may regulate TMEM63 channel function.
• These findings offer mechanistic insights into TMEM63 channelopathies and their underlying molecular basis.