title: Dynamic activity of lipid droplets: protein phosphorylation and GTP-mediated protein translocation.
abstract: Lipid droplet is a cellular organelle with a neutral lipid core surrounded by a phospholipid monolayer and coated with structural as well as functional proteins. The determination of these proteins, especially their functional regulations and dynamic movement on and off droplets, holds a key to resolving the biological functions of the cellular organelle. To address this, we carried out a comprehensive proteomic study that includes a complete proteomic, a phosphoprotein proteomic, and a comparative proteomic analysis using purified lipid droplets and mass spectrometry techniques. The complete proteome identified 125 proteins of which 70 proteins had not been identified on droplets of mammalian cells previously. In phosphoprotein proteomic analysis, 7 functional lipid droplet proteins were determined to be phosphorylated, including adipose differentiation related protein (ADRP/ADFP), two Rab proteins, and four lipid metabolism enzymes, including adipose triglyceride lipase (ATGL). To understand the dynamics of lipid droplets, GTP-dependent protein recruitment was analyzed by comparative proteomics. Arf1 and some of its coatomers, three other Arfs, several other small G-proteins including 3 Rabs, and several lipid synthetic enzymes were recruited from cytosol to purified droplets. Together, the present study suggests that lipid droplet is an active and dynamic cellular organelle that governs lipid homeostasis and intracellular trafficking through protein phosphorylation as well as GTP-regulated protein translocation.
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9039, USA.
authors.forename: René
authors.initials: R
authors.lastname: Bartz
authors.forename: John K
authors.initials: JK
authors.lastname: Zehmer
authors.forename: Meifang
authors.initials: M
authors.lastname: Zhu
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Ginette
authors.initials: G
authors.lastname: Serrero
authors.forename: Yingming
authors.initials: Y
authors.lastname: Zhao
authors.forename: Pingsheng
authors.initials: P
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D003412:Cricetulus; D006160:Guanosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D050356:Lipid Metabolism; D013058:Mass Spectrometry / Q000379:methods; D008969:Molecular Sequence Data; D019301:Oleic Acid / Q000494:pharmacology; D015388:Organelles / Q000378:metabolism*; D010750:Phosphoproteins / Q000032:analysis*; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology
chemical_list: D010750:Phosphoproteins; D019301:Oleic Acid; D006160:Guanosine Triphosphate