GMx33: A Novel Family of trans‐Golgi Proteins Identified by Proteomics

• Published in: Traffic (Copenhagen, Denmark) Vol. 1; no. 12; pp. 963 - 975
• Main Authors: Wu, Christine C., Taylor, Randall S., Lane, Diana R., Ladinsky, Mark S., Weisz, Julie A., Howell, Kathryn E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2000
• Subjects: Detergent solubility; immuno‐EM; peripheral Golgi protein; proteomics; trans‐Golgi network; two‐dimensional gel electrophoresis
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/j.1600-0854.2000.11206.x

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. GMx33α 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 GMx33α differentially partitions into all phases of multiple detergent extractions, and two‐dimensional immunoblots reveal that there are multiple differentially modified forms of GMx33α associated with the Golgi, several of which are phosphorylated. Evidence suggests that these post‐translational modifications regulate its association with the Golgi. GMx33α was not found on Golgi budded vesicles, and immuno‐electron microscopy co‐localizes GMx33α 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.