An alliance between lipid transfer proteins and scramblases for membrane expansion.

Membrane growth requires lipid supply, which is usually accomplished by lipid synthesis or vesicular trafficking. In the case of autophagosomes, these principles do not apply. Ghanbarpour et al . postulate that autophagosome expansion relies on non-vesicular lipid delivery from the ER, whereby the activity of a lipid transfer protein (LTP) is directly coupled to scramblase activities in the donor and acceptor bilayers 1 . This new concept opens the possibility that lipid traffic is controlled by scramblases that provide not only specific docking sites for LTPs, thereby directing lipid flow, but also support their activity by overcoming barriers for lipid extraction and deposition.