Class C ABC transporters and Saccharomyces cerevisiae vacuole fusion

Abstract

Membrane fusion is carried out by core machinery that is conserved throughout eukaryotes. This is comprised of Rab GTPases and their effectors, and SNARE proteins, which together are sufficient to drive the fusion of reconstituted proteoliposomes. However, an outer layer of factors that are specific to individual trafficking pathways in vivo regulates the spatial and temporal occurrence of fusion. The homotypic fusion of Saccharomyces cerevisiae vacuolar lysosomes utilizes a growing set of factors to regulate the fusion machinery that include members of the ATP binding cassette (ABC) transporter family. Yeast vacuoles have five class C ABC transporters that are known to transport a variety of toxins into the vacuole lumen as part of detoxifying the cell. We have found that ABCC transporters can also regulate vacuole fusion through novel mechanisms. For instance Ybt1 serves as negative regulator of fusion through its effects on vacuolar Ca²⁺ homeostasis. Additional studies showed that Ycf1 acts as a positive regulator by affecting the efficient recruitment of the SNARE Vam7. Finally, we discuss the potential interface between the translocation of lipids across the membrane bilayer, also known as lipid flipping, and the efficiency of fusion.

Keywords:

• SNARE
• PI3P
• Vam7
• Ycf1
• Ybt1
• Nft1
• Vmr1
• Bpt1
• Ca²⁺ homeostasis
• lipid flipping

Abbreviations:

• ABC, ATP binding cassette
• DAG, diacylglycerol
• HOPS, homotypic fusion and vacuole protein sorting complex
• MDR, multidrug resistance
• MSD, membrane spanning domain
• NBD, nucleotide binding domain
• PA, phosphatidic acid
• PC, phosphatidylcholine
• PE, phosphatidylethanolamine
• PI, phosphatidylinositol
• PI3P, phosphatidylinositol 3-phosphate
• PI(3, 5)P₂, phosphatidylinositol 3, 5-bisphosphate
• PS, phosphatidylserine
• PX, phox homology
• SNARE, soluble N-ethylmaleimide-sensitive factor attachment protein receptors

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank members of the Fratti Lab for the critical reading of the manuscript.

Additional information

Funding

This work was supported by a grant from the National Institutes of Health (GM101132) to RAF.