Membrane curvature sensing and stabilization by the autophagic LC3 lipidation machinery

Abstract

How the highly curved phagophore membrane is stabilized during autophagy initiation is a major open question in autophagosome biogenesis. Here, we use in vitro reconstitution on membrane nanotubes and molecular dynamics simulations to investigate how core autophagy proteins in the LC3 lipidation cascade interact with curved membranes, providing insight into possible roles in regulating membrane shape during autophagosome biogenesis. ATG12-5-16L1 was up to 100-fold enriched on highly curved nanotubes relative to flat membranes. At high surface density, ATG12-5-16L1 binding increased the curvature of the nanotubes. While WIPI2 binding directs membrane recruitment, the amphipathic helix 2 of ATG16L1 is responsible for curvature sensitivity. Molecular dynamics simulations revealed that helix 2 of ATG16L1 inserts shallowly into the membrane, explaining its curvature-sensitive binding to the membrane. These observations show how the binding of the ATG12-5-16L1 complex to the early phagophore rim could stabilize membrane curvature and facilitate autophagosome growth.