title: Constitutive nuclear localization of an alternatively spliced sirtuin-2 isoform.
abstract: Sirtuin-2 (SIRT2), the cytoplasmic member of the sirtuin family, has been implicated in the deacetylation of nuclear proteins. Although the enzyme has been reported to be located to the nucleus during G2/M phase, its spectrum of targets suggests functions in the nucleus throughout the cell cycle. While a nucleocytoplasmic shuttling mechanism has been proposed for SIRT2, recent studies have indicated the presence of a constitutively nuclear isoform. Here we report the identification of a novel splice variant (isoform 5) of SIRT2 that lacks a nuclear export signal and encodes a predominantly nuclear isoform. This novel isoform 5 fails to show deacetylase activity using several assays, both in vitro and in vivo, and we are led to conclude that this isoform is catalytically inactive. Nevertheless, it retains the ability to interact with p300, a known interaction partner. Moreover, changes in intrinsic tryptophan fluorescence upon denaturation indicate that the protein is properly folded. These data, together with computational analyses, confirm the structural integrity of the catalytic domain. Our results suggest an activity-independent nuclear function of the novel isoform.
authors.affiliation: Department of Molecular Biology, University of Bergen, Postbox 7803, 5020 Bergen, Norway. Electronic address: Johannes.Rack@mbi.uib.no.
authors.forename: Johannes G M
authors.initials: JG
authors.lastname: Rack
authors.affiliation: Department of Molecular Biology, University of Bergen, Postbox 7803, 5020 Bergen, Norway. Electronic address: Magali.Vanlinden@mbi.uib.no.
authors.forename: Magali R
authors.initials: MR
authors.lastname: VanLinden
authors.affiliation: Department of Molecular Biology, University of Bergen, Postbox 7803, 5020 Bergen, Norway. Electronic address: Timo.Lutter@mbi.uib.no.
authors.forename: Timo
authors.initials: T
authors.lastname: Lutter
authors.affiliation: Department of Molecular Biology, University of Bergen, Postbox 7803, 5020 Bergen, Norway. Electronic address: Aasland@mbi.uib.no.
authors.forename: Rein
authors.initials: R
authors.lastname: Aasland
authors.affiliation: Department of Molecular Biology, University of Bergen, Postbox 7803, 5020 Bergen, Norway. Electronic address: mathias.ziegler@mbi.uib.no.
authors.forename: Mathias
authors.initials: M
authors.lastname: Ziegler
mesh_terms: D020121:5' Untranslated Regions; D017398:Alternative Splicing; D020134:Catalytic Domain / Q000235:genetics; D002467:Cell Nucleus / Q000201:enzymology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D049790:Nuclear Export Signals; D011487:Protein Conformation; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D056565:Sirtuin 2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D055672:Static Electricity
chemical_list: D020121:5' Untranslated Regions; D049790:Nuclear Export Signals; D020033:Protein Isoforms; D012322:RNA Precursors; D011994:Recombinant Proteins; C474199:SIRT2 protein, human; D056565:Sirtuin 2
keywords: NAD(+)-dependent signaling; localization; molecular genetics; p300; protein structure