EXPLORING HUMAN GOLGIN-45: STRUCTURE, MOLECULAR INTERACTIONS AND BIOMOLECULAR CONDENSATE FORMATION

The Golgi Complex is a eukaryotic organelle that plays a crucial role in the
trafficking, processing, and sorting of proteins and lipids. This organelle has a unique
architecture, consisting of a stack of flattened cisternae interconnected by
tubulovesicular networks. The maintenance of this unique structure is crucial for
Golgi function and depends on a group of proteins known as Golgi Matrix Proteins,
consisting mainly of Golgi Reassembly and Stacking Proteins (GRASPs) and
Golgins. Golgi Matrix Proteins are responsible for the Golgi's architecture however,
the role these proteins play in the overall organization and dynamics remains
unknown. Golgins are a family of proteins predicted to be formed by extended coiled
coils, with a predicted length between 100-600 nm. They bind to the Golgi cisternae
via their carboxyl terminus, interacting directly with the membrane surface or through
a membrane-associated partner. Many mammalian Golgins can efficiently populate a
liquid-like droplet state once they are overexpressed in vivo and dispersed in the
cytosol. It has been shown that protein condensation occurring on the surfaces of
synthetic and cell-derived membrane vesicles induces significant compressive stress
within the membrane plane, which causes the membrane to bend inwards, forming
protein-lined membrane tubules. Since biomolecular condensates can drastically
affect membrane curvature and some Golgins are capable of forming biomolecular
condensates in cells when overexpressed, there may be a direct correlation between
the propensity of Golgi Matrix Proteins to form biomolecular condensates and the
unusual shape of Golgi cisternae. However, there are no studies on the structural
and biophysical characterization of members of the Golgin family, nor a systematic
study on the physical chemistry of the formation of these condensates and the
potential impact of structural modulation of the lipid membrane. Considering the gap
in knowledge of the structural properties of Golgins, this work aims to characterize
one of these members, specifically human Golgin-45.