Lysine desuccinylase SIRT5 binds to cardiolipin and regulates the electron transport chain

Abstract

Edited by George M. Carman SIRT5 is a lysine desuccinylase known to regulate mitochondrial fatty acid oxidation and the urea cycle. Here, SIRT5 was observed to bind to cardiolipin via an amphipathic helix on its N terminus. In vitro, succinyl-CoA was used to succinylate liver mitochondrial membrane proteins. SIRT5 largely reversed the succinyl-CoA-driven lysine succinylation. Quantitative mass spectrometry of SIRT5-treated membrane proteins pointed to the electron transport chain, particularly Complex I, as being highly targeted for desuccinylation by SIRT5. Mitochondrial oxidative energy metabolism is fundamental to human health, and changes in mitochondrial function are now recognized as playing an etiological role in diseases such as cancer, diabetes, and neurodegeneration. Of particular importance to mitochondrial function are the ϳ200 proteins that reside on the inner mitochondrial membrane (IMM).3 IMM proteins include a large family of solute transporters, several ion channels, four electron transport chain (ETC) complexes, and ATP synthase. Additionally, the IMM has many peripherally associated proteins that bind to the membrane electrostatically rather than via transmembrane domains. This group includes enzymes such as carnitine palmitoyltransferase-2, mitochondrial trifunctional protein (MTP), and very-longchain acyl-CoA dehydrogenase (VLCAD), which together catalyze long-chain fatty acid oxidation (FAO). All three show membrane localization through electrostatic binding to cardiolipin on the IMM (1-3). Cardiolipin also appears to facilitate assembly of higher-order ETC "supercomplexes" that mediate maximal respiratory efficiency (4). In an additional layer of complexity, there is increasing evidence that metabolic pathways that directly produce reducing equivalents, such as FAO and the tricarboxylic acid cycle (TCA), can physically interact with the ETC and potentially with each other (5).To date, the factors that regulate metabolic complex assembly and facilitate protein-protein and protein-lipid interactions on the IMM are poorly understood. Reversible post-translational protein modifications such as lysine acylation are widespread in the mitochondria and represent a potential regulatory mechanism for the formation and function of IMM protein complexes. For example, we recently showed that succinylation of three lysine residues in the VLCAD C terminus leads to a complete loss of membrane binding (1). Succinylation converts the positively charged lysine residues to negative charges, thereby disrupting the electrostatic interaction between the amphipathic helix of VLCAD and cardiolipin. Incubation with the mitochondrial desuccinylase SIRT5 restores membrane binding of VLCAD. Mass spectrometry studies have identified SIRT5-targeted lysines on other IMM proteins such as MTP, ADP/ATP translocase, isocitrate dehydrogenase, and hydroxymethylglutaryl-CoA synthase-2 (6 -10), but its role in maintaining the integrity of the IMM proteome has not been directly

Sirtuin 5 is required for mouse survival in response to cardiac pressure overload

“…7B), suggesting that complex formation is normal. This is consistent with previously published findings in SIRT5KO livers (10).…”

“…7D). Supporting this model, SIRT5 was recently described to regulate oxidative phosphorylation via its desuccinylase activity in liver (10), which identified the electron transport chain as the top pathway targeted by SIRT5 and further found that complex II and ATP synthase activities were significantly decreased in mitochondria isolated from SIRT5KO mouse liver.…”

“…SIRT5-mediated desuccinylation has been reported to repress activity of PDH (7) and enhance activity of HMGCS2 (8). SDH activity has been reported to be both repressed by desuccinylation (8,9) and enhanced (10). Aside from these targets, hundreds of sites of lysine succinylation (8), malonylation (11), and glutarylation (5) lack functional characterization.…”

Extranuclear Sirtuins and Metabolic Stress

“…Coordinated function of SIRT3 and SIRT5 in the regulation of ureagenesis agrees well with the regulation of both sirtuin genes by PGC-1α, a fasting-activated transcriptional regulator (2). SIRT5 targets several components of the electron transport chain (140). It was first originally reported that SIRT5 has a suppressive effect on cellular respiration (91).…”

“…It was first originally reported that SIRT5 has a suppressive effect on cellular respiration (91). However, several more recent studies have observed positive effects on oxidative phosphorylation (12,140,143).…”