The Golgi matrix proteins have a high propensity to form liquid droplets

The Golgi complex is an organelle that plays an essential role in the processing and sorting proteins and lipids until their final destination. The organization and function of the Golgi require the so-called Golgi matrix proteins, which exist primarily as fibre-like bridges in the cisterna stacking or connecting cisternae and secretory vesicles. Golgins and GRASPs (Golgi Reassembly and Stacking Protein) are members of this family of matrix proteins and were already shown to be sufficient to generate the Golgi's higher-order architecture by a mechanism independent of the bulk of other Golgi proteins. However, it remains unclear how the Golgi matrix can induce the flattening of the cisternae membrane and how they contribute to the unique fluidity and orientation polarity of the Golgi complex. Recent research in 2020 by P. Ziltener et al. revealed that several mammalian Golgins tend to form liquid droplets through liquid-liquid phase separation (LLPS) when overexpressed in vivo. This discovery suggests that LLPS might play a role in Golgi structuring and fluidity. Building on this, our study demonstrates that LLPS is a widespread property of Golgi matrix proteins, as GRASPs also form droplet-like structures under physiological conditions. 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. Furthermore, our investigation expanded to include GRASPs from lower Eukaryotes, indicating that LLPS propensity and the abundance of intrinsically disordered regions are ancient characteristics of this protein family. In conclusion, our findings shed light on the role of LLPS in Golgi matrix organization and underscore the significance of intrinsic disorder in the functional properties of these proteins.