Structure–function insights into direct lipid transfer between membranes by Mmm1–Mdm12 of ERMES

• Published in: The Journal of cell biology Vol. 217; no. 3; pp. 959 - 974
• Main Authors: Kawano, Shin, Tamura, Yasushi, Kojima, Rieko, Bala, Siqin, Asai, Eri, Michel, Agnès H., Kornmann, Benoît, Riezman, Isabelle, Riezman, Howard, Sakae, Yoshitake, Okamoto, Yuko, Endo, Toshiya
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 05.03.2018; The Rockefeller University Press
• Subjects: Baking yeast; Biological Transport, Active - physiology; Endoplasmic reticulum; Endoplasmic Reticulum - genetics; Endoplasmic Reticulum - metabolism; Fusion protein; Hydrophobicity; Kluyveromyces - genetics; Kluyveromyces - metabolism; Kluyveromyces lactis; Lipids; Liposomes; Membrane Proteins - genetics; Membrane Proteins - metabolism; Membranes; Mitochondria; Mitochondrial Membranes - metabolism; Mitochondrial Proteins - genetics; Mitochondrial Proteins - metabolism; Multiprotein Complexes - genetics; Multiprotein Complexes - metabolism; Mutation; Organelles; Phosphatidylserine; Phospholipids; Phospholipids - genetics; Phospholipids - metabolism; Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Structure-Activity Relationship; Structure-function relationships; Yeast
• ISSN: 0021-9525; 1540-8140; 1540-8140
• DOI: 10.1083/jcb.201704119

The endoplasmic reticulum (ER)–mitochondrial encounter structure (ERMES) physically links the membranes of the ER and mitochondria in yeast. Although the ER and mitochondria cooperate to synthesize glycerophospholipids, whether ERMES directly facilitates the lipid exchange between the two organelles remains controversial. Here, we compared the x-ray structures of an ERMES subunit Mdm12 from Kluyveromyces lactis with that of Mdm12 from Saccharomyces cerevisiae and found that both Mdm12 proteins possess a hydrophobic pocket for phospholipid binding. However in vitro lipid transfer assays showed that Mdm12 alone or an Mmm1 (another ERMES subunit) fusion protein exhibited only a weak lipid transfer activity between liposomes. In contrast, Mdm12 in a complex with Mmm1 mediated efficient lipid transfer between liposomes. Mutations in Mmm1 or Mdm12 impaired the lipid transfer activities of the Mdm12–Mmm1 complex and furthermore caused defective phosphatidylserine transport from the ER to mitochondrial membranes via ERMES in vitro. Therefore, the Mmm1–Mdm12 complex functions as a minimal unit that mediates lipid transfer between membranes.