Hunt MC

References (8)

Title : Regulation of peroxisomal lipid metabolism: the role of acyl-CoA and coenzyme A metabolizing enzymes - Hunt_2014_Biochimie_98_45
Author(s) : Hunt MC , Tillander V , Alexson SE
Ref : Biochimie , 98 :45 , 2014
Abstract : Peroxisomes are nearly ubiquitous organelles involved in a number of metabolic pathways that vary between organisms and tissues. A common metabolic function in mammals is the partial degradation of various (di)carboxylic acids via alpha- and beta-oxidation. While only a small number of enzymes catalyze the reactions of beta-oxidation, numerous auxiliary enzymes have been identified to be involved in uptake of fatty acids and cofactors required for beta-oxidation, regulation of beta-oxidation and transport of metabolites across the membrane. These proteins include membrane transporters/channels, acyl-CoA thioesterases, acyl-CoA:amino acid N-acyltransferases, carnitine acyltransferases and nudix hydrolases. Here we review the current view of the role of these auxiliary enzymes in peroxisomal lipid metabolism and propose that they function in concert to provide a means to regulate fatty acid metabolism and transport of products across the peroxisomal membrane.
ESTHER : Hunt_2014_Biochimie_98_45
PubMedSearch : Hunt_2014_Biochimie_98_45
PubMedID: 24389458

Title : The emerging role of acyl-CoA thioesterases and acyltransferases in regulating peroxisomal lipid metabolism - Hunt_2012_Biochim.Biophys.Acta_1822_1397
Author(s) : Hunt MC , Siponen MI , Alexson SE
Ref : Biochimica & Biophysica Acta , 1822 :1397 , 2012
Abstract : The importance of peroxisomes in lipid metabolism is now well established and peroxisomes contain approximately 60 enzymes involved in these lipid metabolic pathways. Several acyl-CoA thioesterase enzymes (ACOTs) have been identified in peroxisomes that catalyze the hydrolysis of acyl-CoAs (short-, medium-, long- and very long-chain), bile acid-CoAs, and methyl branched-CoAs, to the free fatty acid and coenzyme A. A number of acyltransferase enzymes, which are structurally and functionally related to ACOTs, have also been identified in peroxisomes, which conjugate (or amidate) bile acid-CoAs and acyl-CoAs to amino acids, resulting in the production of amidated bile acids and fatty acids. The function of ACOTs is to act as auxiliary enzymes in the alpha- and beta-oxidation of various lipids in peroxisomes. Human peroxisomes contain at least two ACOTs (ACOT4 and ACOT8) whereas mouse peroxisomes contain six ACOTs (ACOT3, 4, 5, 6, 8 and 12). Similarly, human peroxisomes contain one bile acid-CoA:amino acid N-acyltransferase (BAAT), whereas mouse peroxisomes contain three acyltransferases (BAAT and acyl-CoA:amino acid N-acyltransferases 1 and 2: ACNAT1 and ACNAT2). This review will focus on the human and mouse peroxisomal ACOT and acyltransferase enzymes identified to date and discuss their cellular localizations, emerging structural information and functions as auxiliary enzymes in peroxisomal metabolic pathways.
ESTHER : Hunt_2012_Biochim.Biophys.Acta_1822_1397
PubMedSearch : Hunt_2012_Biochim.Biophys.Acta_1822_1397
PubMedID: 22465940

Title : A peroxisomal acyltransferase in mouse identifies a novel pathway for taurine conjugation of fatty acids - Reilly_2007_FASEB.J_21_99
Author(s) : Reilly SJ , O'Shea EM , Andersson U , O'Byrne J , Alexson SE , Hunt MC
Ref : FASEB Journal , 21 :99 , 2007
Abstract : A wide variety of endogenous carboxylic acids and xenobiotics are conjugated with amino acids, before excretion in urine or bile. The conjugation of carboxylic acids and bile acids with taurine and glycine has been widely characterized, and de novo synthesized bile acids are conjugated to either glycine or taurine in peroxisomes. Peroxisomes are also involved in the oxidation of several other lipid molecules, such as very long chain acyl-CoAs, branched chain acyl-CoAs, and prostaglandins. In this study, we have now identified a novel peroxisomal enzyme called acyl-coenzyme A:amino acid N-acyltransferase (ACNAT1). Recombinantly expressed ACNAT1 acts as an acyltransferase that efficiently conjugates very long-chain and long-chain fatty acids to taurine. The enzyme shows no conjugating activity with glycine, showing that it is a specific taurine conjugator. Acnat1 is mainly expressed in liver and kidney, and the gene is localized in a gene cluster, together with two further acyltransferases, one of which conjugates bile acids to glycine and taurine. In conclusion, these data describe ACNAT1 as a new acyltransferase, involved in taurine conjugation of fatty acids in peroxisomes, identifying a novel pathway for production of N-acyltaurines as signaling molecules or for excretion of fatty acids.
ESTHER : Reilly_2007_FASEB.J_21_99
PubMedSearch : Reilly_2007_FASEB.J_21_99
PubMedID: 17116739
Gene_locus related to this paper: mouse-acnt1

Title : Analysis of the mouse and human acyl-CoA thioesterase (ACOT) gene clusters shows that convergent, functional evolution results in a reduced number of human peroxisomal ACOTs - Hunt_2006_FASEB.J_20_1855
Author(s) : Hunt MC , Rautanen A , Westin MA , Svensson LT , Alexson SE
Ref : FASEB Journal , 20 :1855 , 2006
Abstract : The maintenance of cellular levels of free fatty acids and acyl-CoAs, the activated form of free fatty acids, is extremely important, as imbalances in lipid metabolism have serious consequences for human health. Acyl-coenzyme A (CoA) thioesterases (ACOTs) hydrolyze acyl-CoAs to the free fatty acid and CoASH, and thereby have the potential to regulate intracellular levels of these compounds. We previously identified and characterized a mouse ACOT gene cluster comprised of six genes that apparently arose by gene duplications encoding acyl-CoA thioesterases with localizations in cytosol (ACOT1), mitochondria (ACOT2), and peroxisomes (ACOT3-6). However, the corresponding human gene cluster contains only three genes (ACOT1, ACOT2, and ACOT4) coding for full-length thioesterase proteins, of which only one is peroxisomal (ACOT4). We therefore set out to characterize the human genes, and we show here that the human ACOT4 protein catalyzes the activities of three mouse peroxisomal ACOTs (ACOT3, 4, and 5), being active on succinyl-CoA and medium to long chain acyl-CoAs, while ACOT1 and ACOT2 carry out similar functions to the corresponding mouse genes. These data strongly suggest that the human ACOT4 gene has acquired the functions of three mouse genes by a functional convergent evolution that also provides an explanation for the unexpectedly low number of human genes.
ESTHER : Hunt_2006_FASEB.J_20_1855
PubMedSearch : Hunt_2006_FASEB.J_20_1855
PubMedID: 16940157
Gene_locus related to this paper: human-ACOT1 , human-ACOT2 , human-ACOT4 , human-ACOT6 , mouse-acot1 , mouse-acot2 , mouse-acot3 , mouse-acot4 , mouse-acot5 , mouse-ACOT6

Title : Molecular cloning and characterization of two mouse peroxisome proliferator-activated receptor alpha (PPARalpha)-regulated peroxisomal acyl-CoA thioesterases - Westin_2004_J.Biol.Chem_279_21841
Author(s) : Westin MA , Alexson SE , Hunt MC
Ref : Journal of Biological Chemistry , 279 :21841 , 2004
Abstract : Peroxisomes are organelles that function in the beta-oxidation of long- and very long-chain acyl-CoAs, bile acid-CoA intermediates, prostaglandins, leukotrienes, thromboxanes, dicarboxylic fatty acids, pristanic acid, and xenobiotic carboxylic acids. The very long- and long-chain acyl-CoAs are mainly chain-shortened and then transported to mitochondria for further metabolism. We have now identified and characterized two peroxisomal acyl-CoA thioesterases, named PTE-Ia and PTE-Ic, that hydrolyze acyl-CoAs to the free fatty acid and coenzyme A. PTE-Ia and PTE-Ic show 82% sequence identity at the amino acid level, and a putative peroxisomal type 1 targeting signal of -AKL was identified at the carboxyl-terminal end of both proteins. Localization experiments using green fluorescent fusion protein showed PTE-Ia and PTE-Ic to be localized in peroxisomes. Despite their high level of sequence identity, we show that PTE-Ia is mainly active on long-chain acyl-CoAs, whereas PTE-Ic is mainly active on medium-chain acyl-CoAs. Lack of regulation of enzyme activity by free CoASH suggests that PTE-Ia and PTE-Ic regulate intraperoxisomal levels of acyl-CoA, and they may have a function in termination of beta-oxidation of fatty acids of different chain lengths. Tissue expression studies revealed that PTE-Ia is highly expressed in kidney, whereas PTE-Ic is most highly expressed in spleen, brain, testis, and proximal and distal intestine. Both PTE-Ia and PTE-Ic were highly up-regulated in mouse liver by treatment with the peroxisome proliferator WY-14,643 and by fasting in a peroxisome proliferator-activated receptor alpha-dependent manner. These data show that PTE-Ia and PTE-Ic have different functions based on different substrate specificities and tissue expression.
ESTHER : Westin_2004_J.Biol.Chem_279_21841
PubMedSearch : Westin_2004_J.Biol.Chem_279_21841
PubMedID: 15007068
Gene_locus related to this paper: mouse-acot3 , mouse-acot5

Title : The human bile acid-CoA:amino acid N-acyltransferase functions in the conjugation of fatty acids to glycine - O'Byrne_2003_J.Biol.Chem_278_34237
Author(s) : O'Byrne J , Hunt MC , Rai DK , Saeki M , Alexson SE
Ref : Journal of Biological Chemistry , 278 :34237 , 2003
Abstract : Bile acid-CoA:amino acid N-acyltransferase (BACAT) catalyzes the conjugation of bile acids to glycine and taurine for excretion into bile. By use of site-directed mutagenesis and sequence comparisons, we have identified Cys-235, Asp-328, and His-362 as constituting a catalytic triad in human BACAT (hBACAT) and identifying BACAT as a member of the type I acyl-CoA thioesterase gene family. We therefore hypothesized that hBACAT may also hydrolyze fatty acyl-CoAs and/or conjugate fatty acids to glycine. We show here that recombinant hBACAT also can hydrolyze long- and very long-chain saturated acyl-CoAs (mainly C16:0-C26:0) and by mass spectrometry verified that hBACAT also conjugates fatty acids to glycine. Tissue expression studies showed strong expression of BACAT in liver, gallbladder, and the proximal and distal intestine. However, BACAT is also expressed in a variety of tissues unrelated to bile acid formation and transport, suggesting important functions also in the regulation of intracellular levels of very long-chain fatty acids. Green fluorescent protein localization experiments in human skin fibroblasts showed that the hBACAT enzyme is mainly cytosolic. Therefore, the cytosolic BACAT enzyme may play important roles in protection against toxicity by accumulation of unconjugated bile acids and non-esterified very long-chain fatty acids.
ESTHER : O'Byrne_2003_J.Biol.Chem_278_34237
PubMedSearch : O'Byrne_2003_J.Biol.Chem_278_34237
PubMedID: 12810727
Gene_locus related to this paper: human-BAAT , mouse-BAAT

Title : Acyl-CoA thioesterases belong to a novel gene family of peroxisome proliferator-regulated enzymes involved in lipid metabolism - Hunt_2000_Cell.Biochem.Biophys_32 Spring_317
Author(s) : Hunt MC , Lindquist PJ , Nousiainen S , Huttunen M , Orii K , Svensson TL , Aoyama T , Hashimoto T , Diczfalusy U , Alexson SE
Ref : Cell Biochem Biophys , 32 Spring :317 , 2000
Abstract : Acyl-CoA thioesterases hydrolyze acyl-CoAs to the corresponding free fatty acid plus coenzyme A. The activity is strongly induced in rat and mouse liver after feeding the animals peroxisome proliferators (PPs). To elucidate the role of these enzymes in lipid metabolism, the authors have cloned the cDNAs corresponding to the inducible cytosolic and mitochondrial type I enzymes (CTE-I and MTE-I), and studied tissue expression and nutritional regulation of expression of the mRNAs in mice. The constitutive expression of both mRNAs was low in liver, with CTE-I expressed mainly in kidney and brown adipose tissue, and MTE-I expressed in brown adipose tissue and heart. As expected, the expression in liver of both the CTE-I and MTE-I mRNAs were strongly induced (> 50-fold) by treatment with clofibrate. A similar level of induction was observed by fasting and a time-course study showed that the CTE-I and MTE-I mRNAs were increased already at 6 h after removal of the diet. Refeeding normal chow diet to mice fasted for 24 h normalized the mRNA levels with a T1/2 of about 3-4 h. Feeding mice a fat-free diet further decreased the expression, possibly indicating repression of expression. The strong expression of MTE-I and CTE-I in the heart was increased about 10-fold by fasting. To further characterize these highly regulated enzymes, the authors have cloned the corresponding genes and promoter regions. The structures of the two genes were found to be very similar, consisting of three exons and two introns. Exon-intron borders conform to general consensus sequences, and, especially, the first exon appears to be highly conserved. The promoter regions of both the CTE-I and MTE-I genes contain putative PP response elements, suggesting an involvement of PP-activated receptors in the regulation of these genes.
ESTHER : Hunt_2000_Cell.Biochem.Biophys_32 Spring_317
PubMedSearch : Hunt_2000_Cell.Biochem.Biophys_32 Spring_317
PubMedID: 11330065
Gene_locus related to this paper: mouse-acot1 , mouse-acot2

Title : Peroxisome proliferator-induced long chain acyl-CoA thioesterases comprise a highly conserved novel multi-gene family involved in lipid metabolism - Hunt_1999_J.Biol.Chem_274_34317
Author(s) : Hunt MC , Nousiainen SE , Huttunen MK , Orii KE , Svensson LT , Alexson SE
Ref : Journal of Biological Chemistry , 274 :34317 , 1999
Abstract : Long chain acyl-CoA esters are important intermediates in degradation and synthesis of fatty acids, as well as having important functions in regulation of intermediary metabolism and gene expression. Although the physiological functions for most acyl-CoA thioesterases have not yet been elucidated, previous data suggest that these enzymes may be involved in lipid metabolism by modulation of cellular concentrations of acyl-CoAs and fatty acids. In line with this, we have cloned four highly homologous acyl-CoA thioesterase genes from mouse, showing multiple compartmental localizations. The nomenclature for these genes has tentatively been assigned as CTE-I (cytosolic), MTE-I (mitochondrial), and PTE-Ia and Ib (peroxisomal), based on the identification of putative targeting signals. Although the various isoenzymes show between 67% and 94% identity at amino acid level, each individual enzyme shows a specific tissue expression. Our data suggest that all four genes are located within a very narrow cluster on chromosome 12 in mouse, similar to a sequence cluster on human chromosome 14, which identified four genes homologous to the mouse thioesterase genes. Four related genes were also identified in Caenorhabditis elegans, all containing putative PTS1 targeting signals, suggesting that the ancestral type I thioesterase gene(s) is/are of peroxisomal origin. All four thioesterases are differentially expressed in tissues examined, but all are inducible at mRNA level by treatment with the peroxisome proliferator clofibrate, or during the physiological condition of fasting, both of which conditions cause a perturbation in overall lipid homeostasis. These results strongly support the existence of a novel multi-gene family cluster of mouse acyl-CoA thioesterases, each with a distinct function in lipid metabolism.
ESTHER : Hunt_1999_J.Biol.Chem_274_34317
PubMedSearch : Hunt_1999_J.Biol.Chem_274_34317
PubMedID: 10567408
Gene_locus related to this paper: mouse-acot1 , mouse-acot2 , mouse-acot3 , mouse-acot4