Figure 3.

Proposed mechanism of VPS13 lipid transport at membrane contact sites. Unidirectional transport of bulk lipids by VPS13 proteins may be driven by localized lipid synthesis at donor membranes and scramblase activity on acceptor membranes. Putative lipid synthesis enzymes are shown in teal and green. These enzymes, which may or may not be coupled directly to VPS13 proteins, could provide a source of newly synthesized lipids for bulk transport. A putative scramblase at the acceptor membrane is shown in purple. Scramblases that non-specifically translocate lipids between acceptor membrane leaflets allow membrane expansion to occur. XK, a predicted phospholipid scramblase, has been recently shown to interact with VPS13A [56]. Model not to scale.