Structural basis for lipid transfer by the ATG2A-ATG9A complex.

Area of Science:

• Cellular Biology
• Structural Biology
• Biochemistry

Background:

• Autophagy is a fundamental cellular process involving the formation of double-membrane vesicles called autophagosomes.
• Autophagy-related proteins (ATGs) 2A and 9A play critical roles in autophagosome biogenesis by facilitating lipid transfer and membrane re-equilibration.

Purpose of the Study:

• To determine the cryo-electron microscopy structures of human ATG2A in complex with WIPI4 and the ATG2A-WIPI4-ATG9A complex.
• To elucidate the molecular mechanisms underlying lipid transfer and membrane dynamics during autophagosome formation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to resolve complex structures.
• Molecular dynamics simulations to investigate lipid extraction mechanisms.
• Cryo-electron tomography to analyze ATG2A liposome-binding states.

Main Results:

• Determined high-resolution structures of ATG2A-WIPI4 and ATG2A-WIPI4-ATG9A complexes.
• Proposed a mechanism for lipid extraction from donor membranes.
• Revealed a 3:1 stoichiometry of ATG9A-ATG2A, aligning ATG9A's pore with ATG2A's lipid transfer cavity.
• Observed ATG2A tethering lipid vesicles in various orientations.

Conclusions:

• Provides a molecular framework for phagophore membrane expansion during autophagy.
• Offers structural insights into the coordinated lipid transport and re-equilibration essential for autophagosome formation.