Macromolecular assemblies regulate nonvesicular phosphatidylserine traffic in yeast

Area of Science:

• Cell Biology
• Membrane Biology
• Lipid Metabolism

Background:

• Phosphatidylserine (PtdSer) is synthesized in the endoplasmic reticulum and mitochondria-associated membrane (MAM).
• PtdSer is transported to decarboxylases Pds1p (mitochondria) and Psd2p (Golgi) via non-vesicular mechanisms.
• Understanding PtdSer transport is key to cellular lipid homeostasis and organelle function.

Purpose of the Study:

• To elucidate the molecular mechanisms regulating non-vesicular phosphatidylserine (PtdSer) transport.
• To identify key proteins and lipids involved in PtdSer trafficking between organelles.
• To characterize the role of specific protein and lipid assemblies in facilitating PtdSer transfer.

Main Methods:

• Genetic analyses of genes regulating PtdSer transport, including MET30, MET4, STT4, PSTB2, and PSD2.
• Biochemical studies to investigate protein and lipid interactions at organelle membranes.
• Reconstitution studies using chemically defined membranes to assess PtdSer donor and acceptor membrane properties.

Main Results:

• MET30-dependent ubiquitination is essential for MAM and mitochondria to act as competent donor and acceptor membranes, respectively.
• Stt4p (phosphatidylinositol 4-kinase) produces phosphatidylinositol 4-phosphate (PtdIns4P), a necessary lipid for PtdSer transport.
• PstB2p and Psd2p, along with anionic lipids like PtdSer, PtdIns4P, and phosphatidic acid, form efficient donor membrane domains for PtdSer transfer.

Conclusions:

• Non-vesicular PtdSer transport relies on specific protein and lipid assemblies at organelle interfaces.
• Macromolecular complexes facilitate docking between donor and acceptor membranes, enabling efficient phospholipid transport.
• These findings reveal intricate mechanisms governing lipid trafficking and organelle communication.