SIRT6 regulates TNF-α secretion through hydrolysis of long-chain fatty acyl lysine

Abstract

The Sir2 family of enzymes or sirtuins are known as nicotinamide adenine dinucleotide (NAD)-dependent deacetylases1 and have been implicated in the regulation of transcription, genome stability, metabolism, and lifespan2, 3. However, four of the seven mammalian sirtuins have very weak deacetylase activity in vitro. Here we show that human Sirt6 efficiently removes long chain fatty acyl groups, such as myristoyl, from lysine residues. The crystal structure of Sirt6 reveals a large hydrophobic pocket that can accommodate long chain fatty acyl groups. We demonstrate further that Sirt6 promotes the secretion of tumor necrosis factor α (TNFα) by removing the fatty acyl modification on K19 and K20 of TNFα. Protein lysine fatty acylation has been known to occur in mammalian cells, but the function and regulatory mechanisms of this modification were unknown. Our data suggest that protein lysine fatty acylation is a novel mechanism that regulates protein secretion. The discovery of Sirt6 as an enzyme that controls protein lysine fatty acylation provides new opportunities to investigate the physiological function of the previously ignored protein posttranslational modification.

Activation of the Protein Deacetylase SIRT6 by Long-chain Fatty Acids and Widespread Deacylation by Mammalian Sirtuins

“…First, the activity of SIRT6 was assessed using an excess of peptide (5 mM (Fig. 1B), respectively, consistent with a prior study (13). In addition, SIRT6 was able to deacylate the decanoyl (96%) and dodecanoyl (98%) groups from lysine residues.…”

“…Consistent with this idea, Jiang et al (13) demonstrated recently that SIRT6 preferentially hydrolyzes long-chain fatty acyl groups, including myristoyl and palmitoyl groups, from lysine residues. A crystal structure of SIRT6 bound to a myristoylated peptide supported this observation.…”

“…Sirtuins-It was recently reported that SIRT6 preferentially hydrolyzes long-chain fatty acyl (myristoyl and palmitoyl groups), relative to deacetylation (13). Here we investigated whether such long-chain deacylation activity was specific to SIRT6 or whether this is a general feature of mammalian sirtuins.…”

“…This structure revealed a long acyl chain binding cleft. Comparing SIRT6 crystal structures with bound and unbound myristoylated peptide revealed conformational differences, adopting a more canonical sirtuin fold when myristoylated peptide is bound (13,19). We hypothesized that this acyl group binding pocket might bind FFAs, and if such binding could induce closure of the splayed SIRT6 subdomains, then SIRT6 might show stimulated deacetylation activity.…”

“…However, several prior studies indicated that SIRT6 acted through deacetylation of histone marks H3K9Ac (14) and H3K56Ac (15), which modulated HIF1-␣-dependent (16), NF-B-dependent (17), and c-Myc-dependent (3) pathways. In cells, the ability of SIRT6 to promote deacetylation of histones and non-histone proteins (18) seemed at odds with the low in vitro deacetylation rates (13,19) and with the recently described demyristoylation activity (13). X-ray structural analysis of SIRT6 suggested that the low deacetylase activity stems from a splayed configuration between the Rossmann fold domain and the zinc binding subdomain (19).…”