Cooper Helen M, Huang Jing-Yi, Verdin Eric, Spelbrink Johannes N
University of Tampere, Institute of Medical Technology and Tampere University Hospital, Tampere, Finland.
PLoS One. 2009;4(3):e4986. doi: 10.1371/journal.pone.0004986. Epub 2009 Mar 31.
Mammals have seven NAD-dependent protein deacetylases. These proteins, called sirtuins, are homologous to yeast Sir2, and are emerging as important regulators of lifespan and intermediary metabolism. Three mammalian sirtuins, SIRT3-5 are mitochondrial. Sirtuins are highly conserved between species, yet mouse SIRT3 was reported to be markedly shorter than its human counterpart and to lack the N-terminal mitochondrial targeting signal present in the human protein.
We have isolated a novel mouse SIRT3 splice variant. This cDNA contains two translation initiation codons upstream of the originally reported start site. We show, using immunofluorescence and protein expression analysis that these longer variants are expressed and efficiently targeted to mitochondria, and that the processed forms of these longer variants are identical in size to the endogenous mouse SIRT3. We also show that the previously described form of SIRT3 is not mitochondrial.
Our observations point to a high level of conservation of SIRT3 as a mitochondrial protein in mice and human and indicate that several previous studies, which addressed mouse Sirt3 function, need to be re-evaluated.
哺乳动物有七种依赖烟酰胺腺嘌呤二核苷酸（NAD）的蛋白质脱乙酰酶。这些蛋白质被称为沉默调节蛋白（sirtuins），与酵母Sir2同源，并且正成为寿命和中间代谢的重要调节因子。三种哺乳动物沉默调节蛋白SIRT3 - 5定位于线粒体。沉默调节蛋白在物种间高度保守，然而据报道小鼠SIRT3明显短于其人类对应物，并且缺乏人类蛋白质中存在的N端线粒体靶向信号。
我们分离出一种新的小鼠SIRT3剪接变体。该cDNA在最初报道的起始位点上游包含两个翻译起始密码子。我们通过免疫荧光和蛋白质表达分析表明，这些较长的变体被表达并有效地靶向线粒体，并且这些较长变体的加工形式在大小上与内源性小鼠SIRT3相同。我们还表明，先前描述的SIRT3形式不是线粒体蛋白。
我们的观察结果表明，SIRT3作为小鼠和人类中的线粒体蛋白具有高度保守性，并表明之前几项关于小鼠Sirt3功能的研究需要重新评估。
