Mechanistic Understanding of Post-Translational Membrane Protein Targeting

PROJECT SUMMARY / ABSTRACT The goal of the proposed study is to understand how cells accurately deliver and insert an essential class of membrane proteins known as tail-anchored proteins (TAs) into the endoplasmic reticulum (ER) membrane. TAs participate in a wide range of important cellular functions including vesicle transport, regulation of apoptosis, and protein quality control. While it is critical for their functions that newly synthesized TAs are localized to appropriate membranes, the details of how cells achieve this spatial organization is not clearly understood. To fill this current knowledge gap, the study proposed here aims to dissect the molecular mechanism of the `Guided Entry of Tail- anchored proteins' (GET) pathway, which guides newly synthesized TAs to the ER membrane. The overarching goal of this proposal is to visualize and understand the major molecular event of the GET pathway. This will be achieved by utilizing cryo-electron microscopy to obtain snapshots of key protein complexes in action, and by complementary protein-protein interaction and TA- insertion studies. More specifically, this study will investigate how the `pre-targeting complex' of the GET pathway captures and commits newly synthesized TAs to the ER-bound path, and once at the ER membrane how the Get1/2 insertase complex inserts TAs into the lipid-bilayer. Together, these multi-disciplinary approaches will enhance our understanding of how cells achieve accuracy and fidelity of TA-targeting, which is essential not only for TA functions but also for maintaining functional ER membrane. Furthermore, these studies will provide valuable insight into various human diseases such as diabetes, cancer and congenital heart disease that have been linked to defective GET pathway.