Interactome map uncovers phosphatidylserine transport by oxysterol-binding proteins.
The internal organization of eukaryotic cells into functionally specialized, membrane-delimited organelles of unique composition implies a need for active, regulated lipid transport. Phosphatidylserine (PS), for example, is synthesized in the endoplasmic reticulum and then preferentially associates--through mechanisms not fully elucidated--with the inner leaflet of the plasma membrane. Lipids can travel via transport vesicles. Alternatively, several protein families known as lipid-transfer proteins (LTPs) can extract a variety of specific lipids from biological membranes and transport them, within a hydrophobic pocket, through aqueous phases. Here we report the development of an integrated approach that combines protein fractionation and lipidomics to characterize the LTP-lipid complexes formed in vivo. We applied the procedure to 13 LTPs in the yeast Saccharomyces cerevisiae: the six Sec14 homology (Sfh) proteins and the seven oxysterol-binding homology (Osh) proteins. We found that Osh6 and Osh7 have an unexpected specificity for PS. In vivo, they participate in PS homeostasis and the transport of this lipid to the plasma membrane. The structure of Osh6 bound to PS reveals unique features that are conserved among other metazoan oxysterol-binding proteins (OSBPs) and are required for PS recognition. Our findings represent the first direct evidence, to our knowledge, for the non-vesicular transfer of PS from its site of biosynthesis (the endoplasmic reticulum) to its site of biological activity (the plasma membrane). We describe a new subfamily of OSBPs, including human ORP5 and ORP10, that transfer PS and propose new mechanisms of action for a protein family that is involved in several human pathologies such as cancer, dyslipidaemia and metabolic syndrome.
European Molecular Biology Laboratory, EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
Kenji
K
Maeda
Kanchan
K
Anand
Antonella
A
Chiapparino
Arun
A
Kumar
Mattia
M
Poletto
Marko
M
Kaksonen
Anne-Claude
AC
Gavin
D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D050171:Dyslipidemias / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D024821:Metabolic Syndrome / Q000378:metabolism; D009369:Neoplasms / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism*; D010802:Phylogeny; D060066:Protein Interaction Maps; D011987:Receptors, Steroid / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D000098825:Oxysterol Binding Proteins
D002352:Carrier Proteins; D010718:Phosphatidylserines; D011987:Receptors, Steroid; D029701:Saccharomyces cerevisiae Proteins; C030363:lipid transfer protein; D000098825:Oxysterol Binding Proteins