ESCRT-III drives the final stages of CUPS maturation for unconventional protein secretion

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Abstract

The unconventional secretory pathway exports proteins that bypass the endoplasmic reticulum. In Saccharomyces cerevisiae, conditions that trigger Acb1 secretion via this pathway generate a Grh1 containing compartment composed of vesicles and tubules surrounded by a cup-shaped membrane and collectively called CUPS. Here we report a quantitative assay for Acb1 secretion that reveals requirements for ESCRT-I, -II, and -III but, surprisingly, without the involvement of the Vps4 AAA-ATPase. The major ESCRT-III subunit Snf7 localizes transiently to CUPS and this was accelerated in vps4Δ cells, correlating with increased Acb1 secretion. Microscopic analysis suggests that, instead of forming intraluminal vesicles with the help of Vps4, ESCRT-III/Snf7 promotes direct engulfment of preexisting Grh1 containing vesicles and tubules into a saccule to generate a mature Acb1 containing compartment. This novel multivesicular / multilamellar compartment, we suggest represents the stable secretory form of CUPS that is competent for the release of Acb1 to cells exterior.

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Amy J Curwin

Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain

Competing interests
No competing interests declared.
Nathalie Brouwers

Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain

Competing interests
No competing interests declared.
Manuel Alonso Adell

Division of Cell Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria

Competing interests
No competing interests declared.
David Teis

Division of Cell Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria

Competing interests
No competing interests declared.
Gabriele Turacchio

Institute of Protein Biochemistry, National Research Council of Italy, Naples, Italy

Competing interests
No competing interests declared.
Seetharaman Parashuraman

Institute of Protein Biochemistry, National Research Council of Italy, Naples, Italy

Competing interests
No competing interests declared.
Paolo Ronchi

Electron Microscopy Core Facility, European Molecular Biology Laboratory, Heidelberg, Germany

Competing interests
No competing interests declared.
Vivek Malhotra

Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain

For correspondence
vivek.malhotra@crg.eu

Competing interests
Vivek Malhotra, Senior editor, eLife.

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