Investigating Structural Determinants for Protein Condensate Formation in the Saccharomyces cerevisiae GRASP

Liquid-liquid phase separation occurs in mixtures with multiple components, spontaneously separating into two liquid phases. This phenomenon has been studied since the 20th century in fields such as chemistry and physics, and it is currently garnering significant interest in molecular biology, particularly in the study of biomolecular condensates. These condensates are formed by proteins and other biomolecules through homotypic or heterotypic interactions, playing crucial roles in cellular regulation and maintenance. Recent studies from our group have shown that Golgi matrix proteins have a strong propensity to form protein condensates. GRASP family proteins are peripheral membrane proteins with structures divided into two PDZ domains, named PDZ1 and PDZ2. The PDZ1 domain is structured and conserved across species, while the PDZ2 domain is an intrinsically disordered region (IDR) with high malleability, facilitating homotypic interactions. Additionally, GRASP proteins play an important role in unconventional protein secretion (UPS). To gain insight into the underlying factors responsible for this propensity, we employed biophysical and microscopy techniques, mapping the structural elements in GRASPs that contribute to LLPS. Our studies focus on the GRASP homolog of Saccharomyces cerevisiae (Grh1), a model organism, to understand which structural sequences determine the functional formation of protein condensates within the cell and how these structures are linked to unconventional secretion.