Origin and significance of membrane asymmetry in yeast

Abstract

Most plasma membranes display asymmetric lipid distributions with the aminophospholipids concentrated in the cytosolic leaflet. This arrangement is critical for cell survival in multicellular organisms but it's purpose for the functioning of individual cells is unclear. A general view is that membrane asymmetry is created by aminophospholipid translocases (APLTs) that use ATP hydrolysis to flip PS and PE from the external to the cytosolic leaflet. The identity of APLTs is not known but prime candidates are members of the P4 subfamily of P‐type ATPases. A systematic analysis of these proteins in budding yeast revealed that: P4 ATPases are essential for aminophospholipid transport and asymmetry; asymmetry is not created at the plasma membrane but rather when membrane flows through the Golgi; loss of P4 ATPase function perturbs vesicle formation in the late secretory and endocytic pathway; P4 ATPases interact with proteins implicated in coat recruitment. Our current work focuses on how P4 ATPases contribute to vesicle formation. As a first approach, we set out to purify and reconstitute P4 ATPases in giant liposomes to test whether these proteins can drive membrane vesiculation. As a complementary approach, we use a proteomics‐based strategy to identify P4 ATPase binding partners that control lipid transport in relation to other aspects of vesicle formation like coat recruitment and cargo sorting.