GRASP55 regulates intra‐Golgi localization of glycosylation enzymes to control glycosphingolipid biosynthesis

Abstract

The Golgi apparatus, the main glycosylation station of the cell, consists of a stack of discontinuous cisternae. Glycosylation enzymes are usually concentrated in one or two specific cisternae along the cis‐trans axis of the organelle. How such compartmentalized localization of enzymes is achieved and how it contributes to glycosylation are not clear. Here, we show that the Golgi matrix protein GRASP55 directs the compartmentalized localization of key enzymes involved in glycosphingolipid (GSL) biosynthesis. GRASP55 binds to these enzymes and prevents their entry into COPI‐based retrograde transport vesicles, thus concentrating them in the trans‐Golgi. In genome‐edited cells lacking GRASP55, or in cells expressing mutant enzymes without GRASP55 binding sites, these enzymes relocate to the cis‐Golgi, which affects glycosphingolipid biosynthesis by changing flux across metabolic branch points. These findings reveal a mechanism by which a matrix protein regulates polarized localization of glycosylation enzymes in the Golgi and controls competition in glycan biosynthesis.

Comparison of the Cisterna Maturation-Progression Model with the Kiss-and-Run Model of Intra-Golgi Transport: Role of Cisternal Pores and Cargo Domains

“…Golgi-resident proteins were also depleted in COPI vesicles visible in S. cerevisiae [ 23 ]. These data appear to contradict data published by Martinez-Menarguez et al [ 52 ], Gilchrist et al [ 51 ], Rizzo et al [ 53 ], and Pothukuchi et al [ 54 ]. We analysed these data in detail and demonstrated that they could also be interpreted from the point of view of the CMPM ([ 38 ], see below).…”

Role of Globotriaosylceramide in Physiology and Pathology

“…Otherwise, Golgi matrix protein GRASP55 prevents the retrograde transport of glycosyltransferases, retaining these enzymes in the trans Golgi. Therefore, a balance between the actions of GOLPH3 and GRASP55 determines the localization and levels of intra-Golgi glycosyltransferases ( Pothukuchi et al, 2021 ).…”

Critical Determinants in ER-Golgi Trafficking of Enzymes Involved in Glycosylation

“…GnT1IP-L can interact directly with GlcNAcT-I, causing its mislocalization from the medial-Golgi to the ER, ERGIC, and cis-Golgi [ 114 ]. Golgi-resident GRASP55 regulated the subcellular localization of glycosylation protein involved in glycosphingolipid biosynthesis by direct interaction [ 115 ]. The L95LGV98 sequence in the GRASP domain of GRASP55 interacted with the cytosolic tail of GlcCer synthase (GCS), which catalyzes the critical step in glycosphingolipid biosynthesis [ 115 ].…”

“…Golgi-resident GRASP55 regulated the subcellular localization of glycosylation protein involved in glycosphingolipid biosynthesis by direct interaction [ 115 ]. The L95LGV98 sequence in the GRASP domain of GRASP55 interacted with the cytosolic tail of GlcCer synthase (GCS), which catalyzes the critical step in glycosphingolipid biosynthesis [ 115 ]. The direct binding with GRASP55 promoted the correct subcellular localization of GCS by preventing GCS from entering in the retrograde transportation [ 115 ].…”

“…The L95LGV98 sequence in the GRASP domain of GRASP55 interacted with the cytosolic tail of GlcCer synthase (GCS), which catalyzes the critical step in glycosphingolipid biosynthesis [ 115 ]. The direct binding with GRASP55 promoted the correct subcellular localization of GCS by preventing GCS from entering in the retrograde transportation [ 115 ]. The GTP exchange factor GBF1 facilitated the phosphorylation of Arf1-GDP, and the Src tyrosine kinase (Src) played an essential role in the ARF GTP formation [ 116 ].…”