Human brown fat inducible thioesterase variant 2 cellular localization and catalytic function

Prediction of mitochondrial targeting signals and their cleavage sites

In this chapter we survey prediction tools and computational methods for the prediction of amino acid sequence elements which target proteins to the mitochondria. We will primarily focus on the prediction of N-terminal mitochondrial targeting signals (MTSs) and their N-terminal cleavage sites by mitochondrial peptidases. We first give practical details useful for using and installing some prediction tools. Then we describe procedures for preparing datasets of MTS containing proteins for statistical analysis or development of new prediction methods. Following that we lightly survey some of the computational techniques used by prediction tools. Finally, after discussing some caveats regarding the reliability of such methods to predict the effects of mutations on MTS function; we close with a discussion of possible future directions of computer prediction methods related to mitochondrial proteins.

Acetyl-CoA metabolic accumulation promotes hepatocellular carcinoma metastasis via enhancing CXCL1-dependent infiltration of tumor-associated neutrophils

High levels of acetyl-CoA are considered a key metabolic feature of metastatic cancers. However, the impacts of acetyl-CoA metabolic accumulation on cancer microenvironment remodeling are poorly understood. In this study, using human hepatocellular carcinoma (HCC) tissues and orthotopic xenograft models, we found a close association between high acetyl-CoA levels in HCCs, increased infiltration of tumor-associated neutrophils (TANs) in the cancer microenvironment and HCC metastasis. Cytokine microarray and enzyme-linked immunosorbent assays (ELISA) revealed the crucial role of the chemokine (C-X-C motif) ligand 1(CXCL1). Mechanistically, acetyl-CoA accumulation induces H3 acetylation-dependent upregulation of CXCL1 gene expression. CXCL1 recruits TANs, leads to neutrophil extracellular traps (NETs) formation and promotes HCC metastasis. Collectively, our work linked the accumulation of acetyl-CoA in HCC cells and TANs infiltration, and revealed that the CXCL1-CXC receptor 2 (CXCR2)-TANs-NETs axis is a potential target for HCCs with high acetyl-CoA levels.

Evolutionary relationship analysis of STARD gene family and VvSTARD5 improves tolerance of salt stress in transgenic tomatoes

The steroidogenic acute regulatory protein-related lipid transfer domain (STARD) forms a protein that can bind membrane-derived phospholipid second messengers and plasma membranes. Although it has been reported in many plants, the evolutionary relationship of the STARD gene family has not been systematically analyzed, and functions of the HD-START and HD-START-MEKHLA domain subgroup genes under hormone and abiotic stress are also unclear in grapes. This study identified and analyzed 23 VvSTARD genes, which were distinctly divided into five subgroups according to five conserved domain types. The analyses of codon preference, selective pressure, and synteny relationship revealed that grape had higher homology with Arabidopsis compared with rice. Interestingly, the expression levels of VvSTARD genes in subgroups 1, 2, and 3 exhibited significant upregulation under NaCl treatment at 24 h, but VvSTARD genes in subgroups 4 and 5 were upregulated under methyl jasmonate (MeJA) treatment at 24 h. The subcellular localization showed that VvSTARD5 was localized in the nucleus. Additionally, under NaCl treatment at 24 h, there were an obvious decrease in the relative electrical leakages and the content of malondialdehyde (MDA), while the relative expression level of VvSTARD5 and content of proline were obviously enhanced in three transgenic lines. Therefore, the overexpression of VvSTARD5 greatly increased the salt tolerance of transgenic tomatoes. Collectively, this study preliminarily explores the comprehensive function of the STARD gene family in grapes and verifies the function of VvSTARD5 in response to salt.

Genome-wide identification and expression analysis of the EXO70 gene family in grape (Vitis vinifera L)

EXO70 is the pivotal protein subunit of exocyst, which has a very crucial role in enhancing the shielding effect of the cell wall, resisting abiotic and hormonal stresses. This experiment aims to identify family members of the EXO70 gene family in grape and predict the characteristics of this gene family, so as to lay the foundation of further exploring the mechanism of resisting abiotic and hormone stresses of VvEXO70s. Therefore, the Vitis vinifera ‘Red Globe’ tube plantlet were used as materials. Bioinformatics was used to inquire VvEXO70 genes family members, gene structure, system evolution, cis-acting elements, subcellular and chromosomal localization, collinearity, selective pressure, codon bias and tissue expression. All of VvEXO70s had the conserved pfam03081 domain which maybe necessary for interacting with other proteins. Microarray analysis suggested that most genes expressed to varying degrees in tendrils, leaves, seeds, buds, roots and stems. Quantitative Real-Time PCR (qRT-PCR) showed that the expression levels of all genes with 5 mM salicylic acid (SA), 0.1 mM methy jasmonate (MeJA), 20% PEG6000 and 4 °C for 24 h were higher than for 12 h. With 20% PEG6000 treatment about 24 h, the relative expression of VvEXO70-02 was significantly up-regulated and 361 times higher than CK. All genes’ relative expression was higher at 12 h than that at 24 h after treatment with 7 mM hydrogen peroxide (H₂O₂) and 0.1 mM ethylene (ETH). In conclusion, the expression levels of 14 VvEXO70 genes are distinguishing under these treatments, which play an important role in the regulation of anti-stress signals in grape. All of these test results provide a reference for the future research on the potential function analysis and plant breeding of VvEXO70 genes.

Allosteric regulation of thioesterase superfamily member 1 by lipid sensor domain binding fatty acids and lysophosphatidylcholine

Nonshivering thermogenesis occurs in brown adipose tissue to generate heat in response to cold ambient temperatures. Thioesterase superfamily member 1 (Them1) is transcriptionally up-regulated in brown adipose tissue upon exposure to the cold and suppresses thermogenesis in order to conserve energy reserves. It hydrolyzes long-chain fatty acyl-CoAs that are derived from lipid droplets, preventing their use as fuel for thermogenesis. In addition to its enzymatic domains, Them1 contains a C-terminal StAR-related lipid transfer (START) domain with unknown ligand or function. By complementary biophysical approaches, we show that the START domain binds to long-chain fatty acids, products of Them1's enzymatic reaction, as well as lysophosphatidylcholine (LPC), lipids shown to activate thermogenesis in brown adipocytes. Certain fatty acids stabilize the START domain and allosterically enhance Them1 catalysis of acyl-CoA, whereas 18:1 LPC destabilizes and inhibits activity, which we verify in cell culture. Additionally, we demonstrate that the START domain functions to localize Them1 near lipid droplets. These findings define the role of the START domain as a lipid sensor that allosterically regulates Them1 activity and spatially localizes it in proximity to the lipid droplet.

Multiple mitochondrial thioesterases have distinct tissue and substrate specificity and CoA regulation, suggesting unique functional roles

Acyl-CoA thioesterases (Acots) hydrolyze fatty acyl-CoA esters. Acots in the mitochondrial matrix are poised to mitigate β-oxidation overload and maintain CoA availability. Several Acots associate with mitochondria, but whether they all localize to the matrix, are redundant, or have different roles is unresolved. Here, we compared the suborganellar localization, activity, expression, and regulation among mitochondrial Acots (Acot2, -7, -9, and -13) in mitochondria from multiple mouse tissues and from a model of Acot2 depletion. Acot7, -9, and -13 localized to the matrix, joining Acot2 that was previously shown to localize there. Mitochondria from heart, skeletal muscle, brown adipose tissue, and kidney robustly expressed Acot2, -9, and -13; Acot9 levels were substantially higher in brown adipose tissue and kidney mitochondria, as was activity for C4:0-CoA, a unique Acot9 substrate. In all tissues, Acot2 accounted for about half of the thioesterase activity for C14:0-CoA and C16:0-CoA. In contrast, liver mitochondria from fed and fasted mice expressed little Acot activity, which was confined to long-chain CoAs and due mainly to Acot7 and Acot13 activities. Matrix Acots occupied different functional niches, based on substrate specificity (Acot9 versus Acot2 and -13) and strong CoA inhibition (Acot7, -9, and -13, but not Acot2). Interpreted in the context of β-oxidation, CoA inhibition would prevent Acot-mediated suppression of β-oxidation, while providing a release valve when CoA is limiting. In contrast, CoA-insensitive Acot2 could provide a constitutive siphon for long-chain fatty acyl-CoAs. These results reveal how the family of matrix Acots can mitigate β-oxidation overload and prevent CoA limitation.

Fatty acid activation in thermogenic adipose tissue

Channeling carbohydrates and fatty acids to thermogenic tissues, including brown and beige adipocytes, have garnered interest as an approach for the management of obesity-related metabolic disorders. Mitochondrial fatty acid oxidation (β-oxidation) is crucial for the maintenance of thermogenesis. Upon cellular fatty acid uptake or following lipolysis from triglycerides (TG), fatty acids are esterified to coenzyme A (CoA) to form active acyl-CoA molecules. This enzymatic reaction is essential for their utilization in β-oxidation and thermogenesis. The activation and deactivation of fatty acids are regulated by two sets of enzymes called acyl-CoA synthetases (ACS) and acyl-CoA thioesterases (ACOT), respectively. The expression levels of ACS and ACOT family members in thermogenic tissues will determine the substrate availability for β-oxidation, and consequently the thermogenic capacity. Although the role of the majority of ACS and ACOT family members in thermogenesis remains unclear, recent proceedings link the enzymatic activities of ACS and ACOT family members to metabolic disorders and thermogenesis. Elucidating the contributions of specific ACS and ACOT family members to trafficking of fatty acids towards thermogenesis may reveal novel targets for modulating thermogenic capacity and treating metabolic disorders.

Deactivating Fatty Acids: Acyl-CoA Thioesterase-Mediated Control of Lipid Metabolism

The cellular uptake of free fatty acids (FFA) is followed by esterification to coenzyme A (CoA), generating fatty acyl-CoAs that are substrates for oxidation or incorporation into complex lipids. Acyl-CoA thioesterases (ACOTs) constitute a family of enzymes that hydrolyze fatty acyl-CoAs to form FFA and CoA. Although biochemically and biophysically well characterized, the metabolic functions of these enzymes remain incompletely understood. Existing evidence suggests regulatory roles in controlling rates of peroxisomal and mitochondrial fatty acyl-CoA oxidation, as well as in the subcellular trafficking of fatty acids. Emerging data implicate ACOTs in the pathogenesis of metabolic diseases, suggesting that better understanding their pathobiology could reveal unique targets in the management of obesity, diabetes, and nonalcoholic fatty liver disease.

Thioesterase superfamily member 1 suppresses cold thermogenesis by limiting the oxidation of lipid droplet-derived fatty acids in brown adipose tissue

OBJECTIVE

Non-shivering thermogenesis in brown adipose tissue (BAT) plays a central role in energy homeostasis. Thioesterase superfamily member 1 (Them1), a BAT-enriched long chain fatty acyl-CoA thioesterase, is upregulated by cold and downregulated by warm ambient temperatures. Them1 (-/-) mice exhibit increased energy expenditure and resistance to diet-induced obesity and diabetes, but the mechanistic contribution of Them1 to the regulation of cold thermogenesis remains unknown.

METHODS

Them1 (-/-) and Them1 (+/+) mice were subjected to continuous metabolic monitoring to quantify the effects of ambient temperatures ranging from thermoneutrality (30 °C) to cold (4 °C) on energy expenditure, core body temperature, physical activity and food intake. The effects of Them1 expression on O2 consumption rates, thermogenic gene expression and lipolytic protein activation were determined ex vivo in BAT and in primary brown adipocytes.

RESULTS

Them1 suppressed thermogenesis in mice even in the setting of ongoing cold exposure. Without affecting thermogenic gene transcription, Them1 reduced O2 consumption rates in both isolated BAT and primary brown adipocytes. This was attributable to decreased mitochondrial oxidation of endogenous but not exogenous fatty acids.

CONCLUSIONS

These results show that Them1 may act as a break on uncontrolled heat production and limit the extent of energy expenditure. Pharmacologic inhibition of Them1 could provide a targeted strategy for the management of metabolic disorders via activation of brown fat.

Acyl-CoA thioesterase 9 (ACOT9) in mouse may provide a novel link between fatty acid and amino acid metabolism in mitochondria

Acyl-CoA thioesterase (ACOT) activities are found in prokaryotes and in several compartments of eukaryotes where they hydrolyze a wide range of acyl-CoA substrates and thereby regulate intracellular acyl-CoA/CoA/fatty acid levels. ACOT9 is a mitochondrial ACOT with homologous genes found from bacteria to humans and in this study we have carried out an in-depth kinetic characterization of ACOT9 to determine its possible physiological function. ACOT9 showed unusual kinetic properties with activity peaks for short-, medium-, and saturated long-chain acyl-CoAs with highest V max with propionyl-CoA and (iso) butyryl-CoA while K cat/K m was highest with saturated long-chain acyl-CoAs. Further characterization of the short-chain acyl-CoA activity revealed that ACOT9 also hydrolyzes a number of short-chain acyl-CoAs and short-chain methyl-branched CoA esters that suggest a role for ACOT9 in regulation also of amino acid metabolism. In spite of markedly different K ms, ACOT9 can hydrolyze both short- and long-chain acyl-CoAs simultaneously, indicating that ACOT9 may provide a novel regulatory link between fatty acid and amino acid metabolism in mitochondria. Based on similar acyl-CoA chain-length specificities of recombinant ACOT9 and ACOT activity in mouse brown adipose tissue and kidney mitochondria, we conclude that ACOT9 is the major mitochondrial ACOT hydrolyzing saturated C2-C20-CoA in these tissues. Finally, ACOT9 activity is strongly regulated by NADH and CoA, suggesting that mitochondrial metabolic state regulates the function of ACOT9.

The Lipid Transfer Protein StarD7: Structure, Function, and Regulation

The steroidogenic acute regulatory (StAR) protein-related lipid transfer (START) domain proteins constitute a family of evolutionarily conserved and widely expressed proteins that have been implicated in lipid transport, metabolism, and signaling. The 15 well-characterized mammalian START domain-containing proteins are grouped into six subfamilies. The START domain containing 7 mRNA encodes StarD7, a member of the StarD2/phosphatidylcholine transfer protein (PCTP) subfamily, which was first identified as a gene overexpressed in a choriocarcinoma cell line. Recent studies show that the StarD7 protein facilitates the delivery of phosphatidylcholine to the mitochondria. This review summarizes the latest advances in StarD7 research, focusing on the structural and biochemical features, protein-lipid interactions, and mechanisms that regulate StarD7 expression. The implications of the role of StarD7 in cell proliferation, migration, and differentiation are also discussed.

Functional characterization of thioesterase superfamily member 1/Acyl-CoA thioesterase 11: implications for metabolic regulation

Thioesterase superfamily member 1 (Them1; synonyms acyl-CoA thioesterase 11 and StarD14) is highly expressed in brown adipose tissue and limits energy expenditure in mice. Them1 is a putative fatty acyl-CoA thioesterase that comprises tandem hot dog-fold thioesterase domains and a lipid-binding C-terminal steroidogenic acute regulatory protein-related lipid transfer (START) domain. To better define its role in metabolic regulation, this study examined the biochemical and enzymatic properties of Them1. Purified recombinant Them1 dimerized in solution to form an active fatty acyl-CoA thioesterase. Dimerization was induced by fatty acyl-CoAs, coenzyme A (CoASH), ATP, and ADP. Them1 hydrolyzed a range of fatty acyl-CoAs but exhibited a relative preference for long-chain molecular species. Thioesterase activity varied inversely with temperature, was stimulated by ATP, and was inhibited by ADP and CoASH. Whereas the thioesterase domains of Them1 alone were sufficient to yield active recombinant protein, the START domain was required for optimal enzyme activity. An analysis of subcellular fractions from mouse brown adipose tissue and liver revealed that Them1 contributes principally to the fatty acyl-CoA thioesterase activity of microsomes and nuclei. These findings suggest that under biological conditions, Them1 functions as a lipid-regulated fatty acyl-CoA thioesterase that could be targeted for the management of metabolic disorders.