Conformational changes in the mitochondrial channel protein, VDAC, and their functional implications

Area of Science:

• Biochemistry
• Structural Biology
• Cell Biology

Background:

• The voltage-dependent, anion-selective channel (VDAC) is crucial for metabolite transport across the mitochondrial outer membrane.
• VDAC interacts with various mitochondrial and cytosolic proteins, influencing cellular processes.
• Structural studies suggest VDAC is a beta-barrel protein, similar to bacterial porins.

Purpose of the Study:

• To elucidate the structural basis of VDAC gating and conformational changes.
• To investigate the role of the N-terminal domain in VDAC function and regulation.
• To understand the mechanism of VDAC's reversible closure.

Main Methods:

• Sequence analysis and circular dichroism spectroscopy to assess secondary structure.
• Electron microscopy of two-dimensional crystals of fungal VDAC.
• Analysis of VDAC gating by membrane potential and pH.

Main Results:

• VDAC undergoes significant conformational changes at low pH (< 5), with decreased beta-sheet and increased alpha-helical content.
• Electron microscopy revealed the lumen size and shape of fungal VDAC, suggesting a mobile N-terminal alpha-helix.
• A model proposes the N-terminal domain's displacement triggers gating and structural rearrangements.

Conclusions:

• VDAC gating is likely mediated by conformational changes involving its N-terminal domain.
• The N-terminal domain's movement may destabilize the beta-barrel structure, leading to channel closure.
• VDAC's gating mechanism differs from bacterial porins, allowing dynamic regulation of mitochondrial transport.