Identification of a Golgi quality control network

• Applicant: Dr. Florian Wilfling
• Subject Area: Biochemistry ; Cell Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 554999331

The Golgi apparatus is the central protein sorting station in cells, with an essential role in maintaining protein homeostasis (proteostasis) for cellular and organismal health. Yet, Golgi quality control (QC) mechanisms that deal with misfolded or orphaned proteins have remained understudied. We have recently identified a Golgi QC that centers around the Defective in SREBP cleavage (Dsc) ubiquitin ligase complex. At the Golgi, the Dsc complex assesses biochemical properties of transmembrane domains (TMDs) and thereby detects orphaned proteins with short TMDs for ubiquitination and selective degradation. Thereby, the Dsc complex prevents the spreading of orphaned proteins from the Golgi into other organelles, and preserves the cellular membrane protein and lipid composition. These findings underscore the pivotal role of the Dsc complex in Golgi QC. Research questions: Based on this knowledge, we propose to identify components that function with the Dsc complex in a QC network at the Golgi. We speculated that Golgi QC would be required for cell survival. Therefore, in our preliminary work, we conducted synthetic lethality screens in yeast, and identified Rer1 as the top negative genetic interactor of Dsc complex mutants. Rer1 is an ER retrieval receptor that returns orphaned membrane proteins from the Golgi back to the ER. Simultaneous loss of Rer1 and the Dsc complex resulted in the collapse of Golgi QC, which entailed the accumulation of membrane proteins across seemingly disrupted Golgi structures and vacuoles, leading to loss of plasma membrane integrity and impaired cell growth. These defects triggered an unusual membrane stress response that involved the biogenesis of a unique multilamellar Golgi derived compartment (GDC) that recruited the TORC2 activated membrane stress kinase Ypk1. Here we will focus on three key questions: (1) How do Rer1 and the Dsc complex work together to maintain Golgi function? (2) How are the multilamellar GDCs formed in response to collapse of Golgi QC? (3) How does Ypk1 signaling at GDCs mitigate membrane stress? By addressing these questions, our project will provide a better understanding of Golgi QC mechanisms and how they govern proteostasis. Approach: We use budding yeast, S. cerevisiae, as the best suited model organism to identify and characterize components of the Golgi QC network. Towards this goal, we combine genetic screens and quantitative proteomics, with biochemical and cell biological approaches, and with correlative cryo-electron tomography. Level of originality: Our research project will identify and characterize on the mechanistic level a multi-layered QC network that operates at the Golgi, maintains organelle architecture and contributes to cellular viability. Hence, our findings will advance the knowledge of cellular quality control and proteostasis - a crucial area in biology in general.

• DFG Programme: Research Grants
• International Connection: Austria
• Cooperation Partner: Professor Dr. David Teis