The GRASP domain in golgi reassembly and stacking proteins: differences and similarities between lower and higher Eukaryotes

The Golgi complex is part of the endomembrane system and is responsible for receiving transport cargos from the endoplasmic reticulum and for sorting and targeting them to their final destination. To perform its function in higher eukaryotic cells, the Golgi needs to be correctly assembled as a flattened membrane sandwich kept together by a protein matrix. The precise mechanism controlling the Golgi cisternae assembly is not yet known, but it is widely accepted that the Golgi Reassembly and Stacking Protein (GRASP) is a main component of the Golgi protein matrix. Unlike mammalian cells, which have two GRASP genes, lower eukaryotes present only one gene and distinct Golgi cisternae assembly. In this study, we performed a set of biophysical studies to get insights on the structural properties of the GRASP domains (DGRASPs) from both human GRASP55 and GRASP65 and compare them with GRASP domains from lower eukaryotes (Saccharomyces cerevisiae and Cryptococcus neoformans). Our data suggest that both human DGRASPs are essentially different from each other and that DGRASP65 is more similar to the subgroup of DGRASPs from lower eukaryotes in terms of its biophysical properties. GRASP55 is present mainly in the Golgi medial and trans faces, which are absent in both fungi, while GRASP65 is located in the cis-Golgi. We suggest that the GRASP65 gene is more ancient and that its paralogue GRASP55 might have appeared later in evolution, together with the medial and trans Golgi faces in mammalians. (AU)