title: Distinct regulation of mitochondrial localization and stability of two human Sirt5 isoforms.
abstract: Seven human Sir2 homologues (sirtuin) have been identified to date. In this study, we clarified the mechanism of subcellular localization of two SIRT5 isoforms (i.e., SIRT5(iso1) and SIRT5(iso2) ) encoded by the human SIRT5 gene and whose C-termini slightly differ from each other. Although both isoforms contain cleavable mitochondrial targeting signals at their N-termini, we found that the cleaved SIRT5(iso2) was localized mainly in mitochondria, whereas the cleaved SIRT5(iso1) was localized in both mitochondria and cytoplasm. SIRT5ΔC, which is composed of only the common domain, showed the same mitochondrial localization as that of SIRT5(iso2) . These results suggest that the cytoplasmic localization of cleaved SIRT5(iso1) is dependent on the SIRT5(iso1) -specific C-terminus. Further analysis showed that the C-terminus of SIRT5(iso2) , which is rich in hydrophobic amino acid residues, functions as a mitochondrial membrane insertion signal. In addition, a de novo protein synthesis inhibition experiment using cycloheximide showed that the SIRT5(iso1) -specific C-terminus is necessary for maintaining the stability of SIRT5(iso1) . Moreover, genome sequence analysis from each organism examined indicated that SIRT5(iso2) is a primate-specific isoform. Taken together, these results indicate that human SIRT5 potentially controls various primate-specific functions via two isoforms with different intracellular localizations or stabilities.
authors.affiliation: Laboratory of Molecular Biochemistry, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Nobuko
authors.initials: N
authors.lastname: Matsushita
authors.forename: Ryo
authors.initials: R
authors.lastname: Yonashiro
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Ogata
authors.forename: Ayumu
authors.initials: A
authors.lastname: Sugiura
authors.forename: Shun
authors.initials: S
authors.lastname: Nagashima
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Fukuda
authors.forename: Ryoko
authors.initials: R
authors.lastname: Inatome
authors.forename: Shigeru
authors.initials: S
authors.lastname: Yanagi
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D004795:Enzyme Stability; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics; D011323:Primates / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D037761:Sirtuins / Q000235:genetics / Q000378:metabolism*
chemical_list: D009687:Nuclear Proteins; D020033:Protein Isoforms; C508544:SIRT5 protein, human; D037761:Sirtuins