Isoform-specific tethering links the Golgi ribbon to maintain compartmentalization.
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.
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.
Timothy
T
Jarvela
Adam D
AD
Linstedt
D001324:Autoantigens / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D000077614:Golgi Matrix Proteins; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011134:Polysaccharides / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D059008:Time-Lapse Imaging; D033921:Vesicular Transport Proteins / Q000378:metabolism
D001324:Autoantigens; C107340:GOLIM4 protein, human; C108705:GORASP1 protein, human; C122048:GORASP2 protein, human; D000077614:Golgi Matrix Proteins; C097741:Golgin subfamily A member 2; D008565:Membrane Proteins; D011134:Polysaccharides; D020033:Protein Isoforms; D033921:Vesicular Transport Proteins