Deciphering co-translational protein folding, assembly and quality control pathways, in health and disease

Introduction

The majority of cellular proteins do not function alone; rather, they act together to achieve concerted functions. Despite the prevalence of protein complexes, little is known about the mechanisms that ensure their correct folding and assembly in the crowded cytoplasm. The importance of the folding challenge is underscored by the growing number of misfolding diseases, often characterized by the aggregation of lonely, unassembled protein subunits.

Ribosome as a Hub

At the critical intersection of synthesis and folding, the ribosome is emerging as a hub, guiding the polypeptide-chain interactions with targeting factors, modifying enzymes, and folding chaperones. We have recently discovered that even the final step of folding, the assembly into complexes, is coordinated with translation.

Co-translational Events

To capture co-translational events in vivo, we developed a ribosome profiling approach. This approach revealed that emerging polypeptide chains are constantly engaged by their partner subunits, protecting them from misfolding (Shiber et al., Nature 2018). However, the mechanisms regulating co-translational assembly pathways remain largely obscure.

Proposal Objectives

In this proposal, we aim to elucidate co-translational protein folding and degradation mechanisms, in health and disease. We will:

1. Identify and characterize novel co-translational degradation pathways by targeting ribosomes synthesizing misfolding-prone subunits.
2. Elucidate the conformational, energetic, and kinetic parameters directing folding and assembly at the atomic level by molecular dynamics.
3. Develop RiboFriend, a single-molecule in vivo approach to elucidate the interplay of chaperones, degradation, and assembly factors during synthesis.

Conclusion

Our collective preliminary results strongly support the feasibility of this proposal. The ability to capture co-translational folding and misfolding pathways in single-molecule resolution can revolutionize our understanding of conformational diseases and the aging process, opening new horizons for therapy.