Abstract
The posttranslational regulation of proteins by lysine (Lys) acetylation has recently emerged to occur not only on histones, but also on organellar proteins in plants and animals. In particular, the catalytic activities of metabolic enzymes have been shown to be regulated by Lys acetylation. The Arabidopsis (Arabidopsis thaliana) genome encodes two predicted sirtuin-type Lys deacetylases, of which only Silent Information Regulator2 homolog (SRT2) contains a predicted presequence for mitochondrial targeting. Here, we have investigated the function of SRT2 in Arabidopsis. We demonstrate that SRT2 functions as a Lys deacetylase in vitro and in vivo. We show that SRT2 resides predominantly at the inner mitochondrial membrane and interacts with a small number of protein complexes mainly involved in energy metabolism and metabolite transport. Several of these protein complexes, such as the ATP synthase and the ATP/ADP carriers, show an increase in Lys acetylation in srt2 loss-of-function mutants. The srt2 plants display no growth phenotype but rather a metabolic phenotype with altered levels in sugars, amino acids, and ADP contents. Furthermore, coupling of respiration to ATP synthesis is decreased in these lines, while the ADP uptake into mitochondria is significantly increased. Our results indicate that SRT2 is important in fine-tuning mitochondrial energy metabolism.
Highlights
The posttranslational regulation of proteins by lysine (Lys) acetylation has recently emerged to occur on histones, and on organellar proteins in plants and animals
We show that Silent Information Regulator2 homolog (SRT2) resides predominantly at the inner mitochondrial membrane and interacts with a small number of protein complexes mainly involved in energy metabolism and metabolite transport
Seven transcript isoforms are predicted for the Arabidopsis SRT2 gene (At5g09230.1–At5g09230.7/SRT2.1–SRT2.7, TAIR10 [The Arabidopsis Information Resource 10]), which are generated from alternative splicing (AS) of the SRT2 precursor mRNA
Summary
The posttranslational regulation of proteins by lysine (Lys) acetylation has recently emerged to occur on histones, and on organellar proteins in plants and animals. We show that SRT2 resides predominantly at the inner mitochondrial membrane and interacts with a small number of protein complexes mainly involved in energy metabolism and metabolite transport Several of these protein complexes, such as the ATP synthase and the ATP/ADP carriers, show an increase in Lys acetylation in srt loss-of-function mutants. Sirtuins have recently emerged as key regulators of life span, cell survival, apoptosis, and metabolism in different heterotrophic organisms (Sauve, 2010; Houtkooper et al, 2012; Sebastián et al, 2012) They are of great interest with regard to energy metabolism, as they are NAD+ dependent and function in a nutrient- and redox-dependent manner (Guarente, 2011). Because the actual biological function of type II sirtuins in mammalian organisms is still under some debate (Newman et al, 2012), and neither sirtuin-specific activity nor function of any plant sirtuin has been demonstrated so far, it was our goal to establish the function of the predicted mitochondrial class II sirtuin SRT2 of Arabidopsis
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