Molecular machines in membrane protein biogenesis

• Applicant: Professor Dr. Matthias Feige, since 4/2023
• Subject Area: Biochemistry ; Structural Biology ; Cell Biology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491930377

Membrane proteins constitute roughly a third of the human proteome. Embedded within cellular membranes, membrane protein biogenesis, folding and degradation are subject to stringent quality control by cellular chaperone networks. How diverse quality control factors cooperate to act on a vast diversity of topologically distinct membrane protein clients is poorly understood. The endoplasmic reticulum membrane protein complex (EMC) has recently emerged as a core component of the membrane protein biogenesis machinery at the ER. Evidence is accumulating that EMC works in interconnected pathways together with known ER quality control factors to triage key steps in membrane protein insertion, folding and degradation. Functional interaction between EMC and ER resident quality control factors offers an attractive framework to understand dependencies of disparate membrane protein clients on EMC for their biogenesis, yet remains challenging to dissect mechanistically in vitro and in vivo. We propose to advance our understanding how EMC:co-factor complexes facilitate membrane protein homeostasis using a synergistic approach between techniques and research groups. Focusing on EMC cooperation with three transmembrane ER co-factors (the lectin CNX, the P5A ATPase and the E3 ligase gp78), we will pursue three specific aims to reveal regulatory principles on the ER quality control hub (ERQCH) centered on EMC. In the first aim, we will map and validate functional interfaces of EMC:co-factor assemblies using mass spectrometric and site-specific in vivo crosslinking. In the second aim, we will determine structures of sub-complexes of the ERQCH involving EMC using in vitro reconstitution and cryo-EM. Finally, the third aim will dissect functions of EMC:co-factor assemblies using cellular assays tailored towards each co-factor and leveraging knock-out cell lines together with structure-guided mutant design. By drawing insight from in vitro reconstitution and studying EMC:co-factor assemblies in a native cellular context, these three aims will propel our understanding of molecular machines in membrane protein biogenesis. Since membrane protein misfolding lies at the heart of many human diseases, we anticipate that our findings on the EMC centered ERQCH will provide answers as to why cells can fail to safeguard membrane protein biogenesis from going awry.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Bastian Braeuning, until 3/2023