Golgi localisation of GMAP210 requires two distinct cis-membrane binding mechanisms

BMC Biol. 2009 Aug 28;7:56. doi: 10.1186/1741-7007-7-56.

Abstract

Background: The Golgi apparatus in mammals appears as a ribbon made up of interconnected stacks of flattened cisternae that is positioned close to the centrosome in a microtubule-dependent manner. How this organisation is achieved and retained is not well understood. GMAP210 is a long coiled-coil cis-Golgi associated protein that plays a role in maintaining Golgi ribbon integrity and position and contributes to the formation of the primary cilium. An amphipathic alpha-helix able to bind liposomes in vitro has been recently identified at the first 38 amino acids of the protein (amphipathic lipid-packing sensor motif), and an ARF1-binding domain (Grip-related Arf-binding domain) was found at the C-terminus. To which type of membranes these two GMAP210 regions bind in vivo and how this contributes to GMAP210 localisation and function remains to be investigated.

Results: By using truncated as well as chimeric mutants and videomicroscopy we found that both the N-terminus and the C-terminus of GMAP210 are targeted to the cis-Golgi in vivo. The ALPS motif was identified as the N-terminal binding motif and appeared concentrated in the periphery of Golgi elements and between Golgi stacks. On the contrary, the C-terminal domain appeared uniformly distributed in the cis-cisternae of the Golgi apparatus. Strikingly, the two ends of the protein also behave differently in response to the drug Brefeldin A. The N-terminal domain redistributed to the endoplasmic reticulum (ER) exit sites, as does the full-length protein, whereas the C-terminal domain rapidly dissociated from the Golgi apparatus to the cytosol. Mutants comprising the full-length protein but lacking one of the terminal motifs also associated with the cis-Golgi with distribution patterns similar to those of the corresponding terminal end whereas a mutant consisting in fused N- and C-terminal ends exhibits identical localisation as the endogenous protein.

Conclusion: We conclude that the Golgi localisation of GMAP210 is the result of the combined action of the two N- and C-terminal domains that recognise different sub-regions of the cis-GA. Based on present and previous data, we propose a model in which GMAP210 would participate in homotypic fusion of cis-cisternae by anchoring the surface of cisternae via its C-terminus and projecting its distal N-terminus to bind the rims or to stabilise tubular structures connecting neighbouring cis-cisternae.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Autoantigens / metabolism
  • Cell Line
  • Centrosome / metabolism
  • Centrosome / ultrastructure
  • Cytoskeletal Proteins
  • Cytosol / metabolism
  • Cytosol / ultrastructure
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum / ultrastructure
  • Gene Expression
  • Golgi Apparatus / metabolism*
  • Golgi Apparatus / ultrastructure
  • Humans
  • Membrane Proteins / metabolism
  • Microscopy, Fluorescence
  • Microscopy, Video
  • Models, Biological
  • Molecular Sequence Data
  • Mutant Chimeric Proteins / chemistry
  • Mutant Chimeric Proteins / metabolism
  • N-Acetyllactosamine Synthase / genetics
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Biosynthesis
  • Protein Interaction Domains and Motifs
  • Protein Transport
  • RNA, Small Interfering
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Retinal Pigment Epithelium
  • Secretory Pathway / physiology*
  • Transfection

Substances

  • Autoantigens
  • Cytoskeletal Proteins
  • GOLGA4 protein, human
  • Membrane Proteins
  • Mutant Chimeric Proteins
  • Nuclear Proteins
  • RNA, Small Interfering
  • Recombinant Fusion Proteins
  • TRIP11 protein, human
  • N-Acetyllactosamine Synthase