Isoform-specific tethering links the Golgi ribbon to maintain compartmentalization

Mol Biol Cell. 2014 Jan;25(1):133-44. doi: 10.1091/mbc.E13-07-0395. Epub 2013 Nov 13.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Autoantigens / metabolism
  • Endoplasmic Reticulum / metabolism
  • Glycosylation
  • Golgi Apparatus / metabolism*
  • Golgi Apparatus / ultrastructure
  • Golgi Matrix Proteins
  • HeLa Cells
  • Humans
  • Intracellular Membranes / metabolism
  • Intracellular Membranes / ultrastructure
  • Membrane Proteins / metabolism*
  • Microscopy, Fluorescence
  • Polysaccharides / metabolism
  • Protein Isoforms / metabolism
  • Protein Processing, Post-Translational
  • Protein Transport
  • Time-Lapse Imaging
  • Vesicular Transport Proteins / metabolism

Substances

  • Autoantigens
  • GOLIM4 protein, human
  • GORASP1 protein, human
  • GORASP2 protein, human
  • Golgi Matrix Proteins
  • Golgin subfamily A member 2
  • Membrane Proteins
  • Polysaccharides
  • Protein Isoforms
  • Vesicular Transport Proteins