Identification of GRASP-specific functions in maintaining Golgi homeostasis using rapid Golgi immunoprecipitation

• Applicant: Dr. Julian Nuechel
• Subject Area: Cell Biology ; Biochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564334266

The Golgi apparatus is an essential cell organelle in the secretory pathway of eukaryotic celsl. Here, secreted proteins are modified and correctly sorted in order to reach the correct destination. The function of the Golgi apparatus depends on the correct protein and lipid composition, as well as the presence of important metabolites that are consumed in the biochemical reactions that take place in the Golgi. The family of Golgi localizing GRASP proteins, GRASP55 and GRASP65, has been previously mainly associated with the morphological integrity of the Golgi. However, in recent years it has been shown that beyond the regulation of Golgi morphology, the GRASP proteins have a major influence on the homeostasis of the Golgi and on the transport processes that take place on the organelle. In fact, it was shown that the GRASP proteins each have unique, non-redundant functions and that their regulation occurs in different ways. GRASP55 was specifically associated with the regulation of unconventional secretion, and an influence of GRASP55 on the sorting of lysosomal proteins at the Golgi was also described. As part of the basic module, I would like to identify the specific functions of the GRASP proteins in Golgi homeostasis by using immune-precipitation-based rapid isolation of the Golgi. Due to the rapid purification procedure, even metabolites and lipids in the Golgi can be detected by mass spectrometry. Purified Golgis from GRASP55 or GRASP65-deficient cells will be analyzed and compared with mass spectrometry in an unbiased manner. Since the Golgi apparatus is also compartmentalized and can be divided into a cis and a trans side, each with specific functions, a purification protocol will be used to achieve sub-Golgi resolution. This will allow us to characterise the role of the GRASP proteins with yet unprecedented detail. The changes, and the upstream regulatory pathways, identified in this way will be further verified using additional cell biological and biochemical methods in order to obtain an expanded picture of the GRASP-dependent regulation of Golgi function and the secretory pathway.

• DFG Programme: Research Grants