SIRT4 Is a Lysine Deacylase that Controls Leucine Metabolism and Insulin Secretion

Abstract

SUMMARY Sirtuins are NAD+-dependent protein deacylases that regulate several aspects of metabolism and aging. In contrast to the other mammalian sirtuins, the primary enzymatic activity of mitochondrial sirtuin 4 (SIRT4) and its overall role in metabolic control has remained enigmatic. Using a combination of phylogenetics, structural biology, and enzymology, we show that SIRT4 removes three acyl moieties from lysine residues – methylglutaryl(MG)-, hydroxymethylglutaryl(HMG)-, and 3-methylglutaconyl(MGc)-lysine. The metabolites leading to these post-translational modifications are intermediates in leucine oxidation, and we show a primary role for SIRT4 in controlling this pathway in mice. Furthermore, we find that dysregulated leucine metabolism in SIRT4KO mice leads to elevated basal and stimulated insulin secretion, which progressively develops into glucose intolerance and insulin resistance. These findings identify a robust enzymatic activity for SIRT4, uncover a mechanism controlling branched-chain amino acid flux, and position SIRT4 as a crucial player maintaining insulin secretion and glucose homeostasis during aging.

A Class of Reactive Acyl-CoA Species Reveals the Non-enzymatic Origins of Protein Acylation

“…In this context, enzymes might have evolved away from having reactive lysines nearby active sites, thereby preventing protein modification, as has been proposed for enzymes in glycolysis (Moellering and Cravatt, 2013). In other cases, protein damage by lysine acylation could be targeted for removal by sirtuins (Anderson et al, 2017). …”

Lipoic acid metabolism and mitochondrial redox regulation

“…Subsequent studies demonstrated that this mechanism was conserved in prokaryotic systems and that OGDH and the glycine cleavage system were also targets of the SIRT4 ortholog, CobB (73). Another study also implicated SIRT4 in regulation of leucine catabolism indicating that BCKDH is likely an additional target of this regulation (74).…”

Mechanism‐Based Inhibitors of the Human Sirtuin 5 Deacylase: Structure–Activity Relationship, Biostructural, and Kinetic Insight

“…[6] Recently, the ability of SIRT4 to cleave the negatively charged ε- N -(3-methylglutaryl)lysine (Kmg) and ε- N -(3-methylglutaconyl)lysine (Kmgc) has also been demonstrated. [7] …”

“…Compound 24 was inspired by work on fluorinated acetamides, [17–18] and inverted amide ( 25 ) as well as Glu(Cbz) 26 have been introduced as side chains previously. [6b, 15c] Finally, 3-methylglutaryl-mimicking [7] analogues ( 27 and 28 ) were prepared along with compound 29 , the thiourea analogue of 10 . Collectively, this exercise showed that thioamide- and thiourea-based compounds were the most potent and thus, compound 29 was chosen for individual optimization of the N-terminal ( 30–44 Scheme 2, green area) and modifications to the C-terminal N-alkyl group ( 45–47 Scheme 2, cyan area).…”