Mitochondrial ATP synthase c-subunit leak channel triggers cell death upon loss of its F₁ subcomplex

Area of Science:

• Mitochondrial bioenergetics
• Cell death mechanisms
• Ion channel biophysics

Background:

• Mitochondrial ATP synthase plays roles beyond energy production, including energy dissipation and cell death.
• The ATP synthase c-ring is implicated as the pore for the mitochondrial permeability transition (mPT) channel.
• mPT activation is observed during excitotoxic ischemic injury.

Purpose of the Study:

• To biophysically characterize the channel activity of the purified human ATP synthase c-ring.
• To elucidate the gating mechanism of the ATP synthase c-subunit leak channel (ACLC).
• To understand the regulation of ACLC opening by cell stress.

Main Methods:

• Purification of human c-ring from eukaryotic and prokaryotic hosts.
• Biophysical characterization of ion channel activity.
• ATP synthase subunit interaction studies.
• ATP synthase c-subunit knockdown experiments.
• Analysis of osmotic changes and channel activity under high calcium conditions.

Main Results:

• Purified c-ring forms a large, multi-conductance, voltage-gated ion channel.
• The F₁ subcomplex inhibits the channel activity, suggesting it acts as the gate.
• Dissociation of F₁ from F_O occurs during excitotoxic neuronal death.
• ATP synthase c-subunit knockdown prevents osmotic changes and eliminates mPT channel activity.
• Channel activity is sensitive to Ca²⁺ and cyclosporin A (CsA).

Conclusions:

• The F₁ subcomplex acts as the gate for the ATP synthase c-subunit leak channel (ACLC).
• ACLC opening is regulated by cell stress in a CypD-dependent manner.
• These findings clarify the gating mechanism and regulation of ACLC during cell death.