Biomolecular condensation of hairpin proteins coordinates cytoplasmic clients to spatially distinct microdomains of the ER membrane

The endoplasmic reticulum (ER) comprises a single continuous membrane network that extends across the entire cell, coordinating diverse cytosolic activities essential for cell survival. Despite this, our understanding of how the ER confines cytosolic proteins to specific regions of its membrane remains tenuous. We have demonstrated that several ER resident hairpin proteins cluster into unique spatial microdomains. Many of these hairpins contain large cytoplasmic-facing intrinsically disordered regions that we believe form biomolecular condensates with specific cytosolic partners. We aim to generate a comprehensive spatial map of ER-hairpin microdomains, subsequently using a series of screening approaches with targeted bioinformatics to identify cytosolic partners. Ultimately we will look to destabilise hairpin:partner interactions and observe the consequences on localisation and function for each partner. Our work will provide a novel molecular mechanism for ER-mediated cytoplasmic organisation, a fundamental cellular process, and set a basis for understanding misregulation of ER:cytoplasmic crosstalk in disease