Vps39 Interacts with Tom40 to Establish One of Two Functionally Distinct Vacuole-Mitochondria Contact Sites
Ayelén González Montoro1, Kathrin Auffarth1, Carina Hönscher1
1Department of Biology/Chemistry, Biochemistry Section University of Osnabrück, Barbarastrasse 13, Osnabrück 49076, Germany.
Abstract:
The extensive subcellular network of membrane contact sites plays central roles in organelle biogenesis and communication, yet the precise contributions of the involved machineries remain largely enigmatic. The yeast vacuole forms a membrane contact site with mitochondria, called vacuolar and mitochondrial patch (vCLAMP). Formation of vCLAMPs involves the vacuolar Rab GTPase Ypt7 and the Ypt7-interacting Vps39 subunit of the HOPS tethering complex. Here, we uncover the general preprotein translocase of the outer membrane (TOM) subunit Tom40 as the direct binding partner of Vps39 on mitochondria. We identify Vps39 mutants defective in TOM binding, but functional for HOPS. Cells that cannot form vCLAMPs show reduced growth under stress conditions and impaired survival upon starvation. Unexpectedly, our mutant analysis revealed the existence of two functionally independent vacuole-mitochondria MCSs: one formed by the Ypt7-Vps39-Tom40 tether and a second one by Vps13-Mcp1, which is redundant with ER-mitochondrial contacts formed by ERMES.
Insights
Researchers identified Tom40 as a key protein in yeast vacuole-mitochondria membrane contact sites (vCLAMPs). This discovery reveals two independent pathways for these crucial organelle connections, impacting cell growth and survival.
Area of Science:
- Cell Biology
- Molecular Biology
- Organelle Biology
Background:
- Membrane contact sites (MCSs) are vital for organelle communication and biogenesis.
- Vacuole-mitochondria MCSs, specifically vacuolar and mitochondrial patch (vCLAMPs), are crucial but their machinery is not fully understood.
- vCLAMP formation involves vacuolar Ypt7 GTPase and the HOPS complex subunit Vps39.
Purpose of the Study:
- To identify the mitochondrial binding partner of Vps39 in vCLAMP formation.
- To investigate the functional significance of the Ypt7-Vps39-mediated vCLAMP.
- To explore alternative pathways for vacuole-mitochondria tethering.
Main Methods:
- Yeast genetics and biochemistry were employed to identify protein interactions.
- Mutagenesis was used to create Vps39 mutants with specific binding defects.
- Cellular growth and survival assays under stress and starvation conditions were performed.
Main Results:
- The general preprotein translocase of the outer membrane (TOM) subunit Tom40 was identified as the direct mitochondrial binding partner of Vps39.
- Vps39 mutants defective in Tom40 binding but functional in HOPS complex assembly were generated.
- Disruption of Ypt7-Vps39-Tom40 mediated vCLAMPs led to reduced growth under stress and impaired starvation survival.
- A second, independent vacuole-mitochondria MCS pathway involving Vps13-Mcp1 was discovered, which is functionally redundant with ER-mitochondrial contacts (ERMES).
Conclusions:
- Tom40 is a direct binding partner of Vps39, mediating a critical vCLAMP pathway.
- Yeast possesses at least two functionally distinct and partially redundant pathways for tethering vacuoles and mitochondria.
- These findings advance our understanding of organelle contact site regulation and cellular stress response.
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