Genetic analysis of the subunit organization and function of the conserved oligomeric golgi (COG) complex: studies of COG5- and COG7-deficient mammalian cells.
The conserved oligomeric Golgi (COG) complex is an eight-subunit (Cog1-8) peripheral Golgi protein involved in Golgi-associated membrane trafficking and glycoconjugate synthesis. We have analyzed the structure and function of COG using Cog1 or Cog2 null Chinese hamster ovary cell mutants, fibroblasts from a patient with Cog7-deficient congenital disorders of glycosylation, and stable Cog5-deficient HeLa cells generated by RNA interference. Although the dilation of some Golgi cisternae in Cog5-deficient cells resembled that observed in Cog1- or Cog2-deficient cells, their global glycosylation defects (less severe) and intracellular processing and function of low density lipoprotein receptors (essentially normal) differed from Cog1- and Cog2-deficient cells. Immunoblotting, gel filtration, and immunofluorescence microscopy analyses of the COG-deficient cells and cell extracts indicated that 1) Cog2-4 and Cog5-7 form stable subcomplexes, 2) Cog1 mediates Golgi association of a Cog2-4 plus Cog8 subcomplex, 3) Cog8 associates stably with both Cog5-7 and Cog1-4 subcomplexes, and thus 4) Cog8 helps assemble the Cog1-4 and Cog5-7 subcomplexes into the complete COG complex. This model of the subunit organization of COG is in excellent agreement with in vitro data presented in an accompanying paper (Ungar, D., Oka, T., Vasile, E., Krieger, M., and Hughson, F. M. (2005) J. Biol. Chem. 280, 32729-32735). Only one or two of the seven Cog1- or Cog2-dependent Golgi membrane proteins called GEARs are also sensitive to Cog5 or Cog7 deficiency, indicating that the COG subunits play distinctive roles in controlling Golgi structure and function.
Oka
Toshihiko
T
Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Vasile
Eliza
E
Penman
Marsha
M
Novina
Carl D
CD
Dykxhoorn
Derek M
DM
Ungar
Daniel
D
Hughson
Frederick M
FM
Krieger
Monty
M
D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D010367:Arachis; D016466:CHO Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics*; D002850:Chromatography, Gel; D006224:Cricetinae; D005347:Fibroblasts / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D037102:Lectins / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D014162:Transfection
D033942:Adaptor Proteins, Vesicular Transport; C115632:COG5 protein, human; D002352:Carrier Proteins; D037102:Lectins; D008565:Membrane Proteins