title: GMx33: a novel family of trans-Golgi proteins identified by proteomics.
abstract: The known functions of the Golgi complex include the sorting, packaging, post-translational modification, and transport of secretory proteins, membrane proteins, and lipids. Other functions still remain elusive to cell biologists. With the goal of identifying novel Golgi proteins, a proteomics project was undertaken to map the major proteins of the organelle using two-dimensional gels, to identify the unknowns using tandem mass spectrometry, and to screen for Golgi residents using GFP-fusion constructs. Multiple unknowns were identified, and the initial characterization of one of these proteins is reported here. GMx33 alpha is a member of a conserved family of cytosolic Golgi-associated proteins with no known homology to any known functional domain or protein. Biochemical analyses show that GMx33 alpha differentially partitions into all phases of multiple detergent extractions, and two-dimensional immunoblots reveal that there are multiple differentially modified forms of GMx33 alpha associated with the Golgi, several of which are phosphorylated. Evidence suggests that these post-translational modifications regulate its association with the Golgi. GMx33 alpha was not found on Golgi budded vesicles, and immuno-electron microscopy co-localizes GMx33 alpha to the trans-face on the same three cisternae as TGN38 in normal rat kidney cells. This work represents the preliminary characterization of a novel family of trans-Golgi-associated proteins.
authors.affiliation: Department of Cellular and Structural Biology, University of Colorado Health Sciences Center, Denver, Colorado, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Wu
authors.forename: R S
authors.initials: RS
authors.lastname: Taylor
authors.forename: D R
authors.initials: DR
authors.lastname: Lane
authors.forename: M S
authors.initials: MS
authors.lastname: Ladinsky
authors.forename: J A
authors.initials: JA
authors.lastname: Weisz
authors.forename: K E
authors.initials: KE
authors.lastname: Howell
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis / Q000737:chemistry*; D002460:Cell Line; D002474:Cell-Free System; D003001:Cloning, Molecular; D003902:Detergents; D015180:Electrophoresis, Gel, Two-Dimensional; D017930:Genes, Reporter; D006023:Glycoproteins; D006801:Humans; D015151:Immunoblotting; D008099:Liver / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000032:analysis; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D020543:Proteome / Q000032:analysis*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000737:chemistry; D016415:Sequence Alignment; D021601:trans-Golgi Network / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D003902:Detergents; C424602:GMx33alpha protein, rat; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D020543:Proteome; D011993:Recombinant Fusion Proteins; C072237:TGOLN2 protein, human; C513045:Tgoln2 protein, rat