title: A palmitoylated RING finger ubiquitin ligase and its homologue in the brain membranes.
abstract: Ubiquitin (Ub) ligation is implicated in active protein metabolism and subcellular trafficking and its impairment is involved in various neurologic diseases. In rat brain, we identified two novel Ub ligases, Momo and Sakura, carrying double zinc finger motif and RING finger domain. Momo expression is enriched in the brain gray matter and testis, and Sakura expression is more widely detected in the brain white matter as well as in many peripheral organs. Both proteins associate with the cell membranes of neuronal and/or glial cells. We examined their Ub ligase activity in vivo and in vitro using viral expression vectors carrying myc-tagged Momo and Sakura. Overexpression of either Momo or Sakura in mixed cortical cultures increased total polyubiquitination levels. In vitro ubiquitination assay revealed that the combination of Momo and UbcH4 and H5c, or of Sakura and UbcH4, H5c and H6 is required for the reaction. Deletion mutagenesis suggested that the E3 Ub ligase activity of Momo and Sakura depended on their C-terminal domains containing RING finger structure, while their N-terminal domains influenced their membrane association. In agreement, Sakura associating with the membrane was specifically palmitoylated. Although the molecular targets of their Ub ligation remain to be identified, these findings imply a novel function of the palmitoylated E3 Ub ligase(s).
authors.affiliation: Department of Molecular Neurobiology, Brain Research Institute, Niigata University, Niigata, Japan.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Araki
authors.forename: Meiko
authors.initials: M
authors.lastname: Kawamura
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Matsuda
authors.forename: Daiji
authors.initials: D
authors.lastname: Kanbe
authors.forename: Kyoko
authors.initials: K
authors.lastname: Ishii
authors.forename: Tomio
authors.initials: T
authors.lastname: Ichikawa
authors.forename: Toshiro
authors.initials: T
authors.lastname: Kumanishi
authors.forename: Tomoki
authors.initials: T
authors.lastname: Chiba
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology*; D002478:Cells, Cultured; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008025:Ligases / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009457:Neuroglia / Q000166:cytology / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009928:Organ Specificity; D019308:Palmitic Acid / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017386:Sequence Homology, Amino Acid; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D012333:RNA, Messenger; D025801:Ubiquitin; D019308:Palmitic Acid; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; C476883:Rffl protein, rat; C476882:Rnf34 protein, rat