Coordination of chaperone interactions that dictate protein folding and trafficking

PROJECT SUMMARY Proteins fold into their 3-dimensional shape with the help of chaperones and other protein folding factors, which together comprise the proteostasis network (PN). During the protein quality control process, transient binding interactions between individual client proteins and proteostasis factors mediate folding into native functional structures, thereby ensuring trafficking to the correct cellular destination or facilitating degradation of detrimental misfolded states. Consequently, imbalances in interactions between proteostasis factors and client proteins result in quality control defects that lead to diverse protein misfolding diseases, including highly prevalent neurodegenerative diseases such as Alzheimer’s and Parkinson’s Disease, and loss-of-function diseases such as Cystic Fibrosis. The folding, maturation, and trafficking of large multi-domain and multi-subunit proteins is a complex and highly client-specific process that depends on engaging the appropriate component of the PN at the correct time. Many proteostasis dependencies for individual client proteins are known, but little is understood about the engagement order and whether correct sequential interactions are required for proper folding and trafficking. We have utilized the power of chemical biology and quantitative proteomics to develop a new tool, time-resolved interactome profiling, to interrogate the dynamics of the interaction between disease-associated protein variants and the PN. We examined the coordination requirement of different proteostasis pathways as they affect protein secretion (thyroglobulin) and loss-of-function protein misfolding (cystic fibrosis transmembrance conductance regulator – CFTR). Loss of secretion of destabilized thyroglobulin variants, a thyroid prohormone, is a leading cause of congenital hypothyroidism while misfolding and pre-mature degradation of CFTR variants is the primary cause of Cystic Fibrosis. We have identified three projects that leverage the utility of our approach and build upon the groundwork laid by our previous findings. These include: 1) Determining the contribution of degradation factors to secretion loss of misfolded thyroglobulin variants. 2) Elucidating the proteostasis dynamics of divergent multipass membrane proteins, and 3) Enhancing the time-resolution of our time-resolved interactomics approach to capture early ER translocation and folding dynamics. Results from our studies will provide significant new insights into how the dynamics of protein folding and trafficking pathways can be manipulated therapeutically for disease intervention.