Isoform-specific tethering links the Golgi ribbon to maintain compartmentalization. Timothy S. Jarvela Adam Linstedt 10.1184/R1/6099818.v1 https://kilthub.cmu.edu/articles/journal_contribution/Isoform-specific_tethering_links_the_Golgi_ribbon_to_maintain_compartmentalization_/6099818 <p>Homotypic membrane tethering by the Golgi reassembly and stacking proteins (GRASPs) is required for the lateral linkage of mammalian Golgi ministacks into a ribbon-like membrane network. Although GRASP65 and GRASP55 are specifically localized to cis and medial/trans cisternae, respectively, it is unknown whether each GRASP mediates cisternae-specific tethering and whether such specificity is necessary for Golgi compartmentalization. Here each GRASP was tagged with KillerRed (KR), expressed in HeLa cells, and inhibited by 1-min exposure to light. Significantly, inactivation of either GRASP unlinked the Golgi ribbon, and the immediate effect of GRASP65-KR inactivation was a loss of cis- rather than trans-Golgi integrity, whereas inactivation of GRASP55-KR first affected the trans- and not the cis-Golgi. Thus each GRASP appears to play a direct and cisternae-specific role in linking ministacks into a continuous membrane network. To test the consequence of loss of cisternae-specific tethering, we generated Golgi membranes with a single GRASP on all cisternae. Remarkably, the membranes exhibited the full connectivity of wild-type Golgi ribbons but were decompartmentalized and defective in glycan processing. Thus the GRASP isoforms specifically link analogous cisternae to ensure Golgi compartmentalization and proper processing.</p> 2014-01-01 00:00:00 Autoantigens Endoplasmic Reticulum Glycosylation Golgi Apparatus HeLa Cells Humans Intracellular Membranes Membrane Proteins Microscopy Fluorescence Polysaccharides Protein Isoforms Protein Processing Post-Translational Protein Transport Time-Lapse Imaging Vesicular Transport Proteins