Human fatty acid synthase: role of interdomain in the formation of catalytically active synthase dimer. (1/69)

The human and animal fatty acid synthases are dimers of two identical multifunctional proteins (M(r) 272,000) arranged in an antiparallel configuration. This arrangement generates two active centers for fatty acid synthesis separated by interdomain (ID) regions and predicts that two appropriate halves of the monomer should be able to reconstitute an active fatty acid synthesizing center. This prediction was confirmed by the reconstitution of the synthase active center by using two heterologously expressed halves of the monomer protein. Each of these recombinant halves of synthase monomer contains half of the ID regions. We show here that the fatty acid synthase activity could not be reconstituted when the ID sequences present in the two recombinant halves are deleted, suggesting that these ID sequences are essential for fatty acid synthase dimer formation. Further, we confirm that the ID sequences are the only regions of fatty acid synthase monomers that showed significant dimer formation, by using the yeast two-hybrid system. These results are consistent with the proposal that the ID region, which has no known catalytic activity, associates readily and holds together the two dynamic active centers of the fatty acid synthase dimer, therefore playing an important role in the architecture of catalytically active fatty acid synthase.  (+info)

Adipogenic signaling in rat white adipose tissue: modulation by aging and calorie restriction. (2/69)

Alterations in adipogenesis could have significant impact on several aging processes. We previously reported that calorie restriction (CR) in rats significantly increases the level of circulating adiponectin, a distinctive marker of differentiated adipocytes, leading to a concerted modulation in the expression of key transcription target genes and, as a result, to increased fatty acid oxidation and reduced deleterious lipid accumulation in other tissues. These findings led us to investigate further the effects of aging on adipocytes and to determine how CR modulates adipogenic signaling in vivo. CR for 2 and 25 months, significantly increased the expression of PPARgamma, C/EBPbeta and Cdk-4, and partially attenuated age-related decline in C/EBPalpha expression relative to rats fed ad libitum (AL). As a result, adiponectin was upregulated at both mRNA and protein levels, resulting in activation of target genes involved in fatty acid oxidation and fatty acid synthesis, and greater responsiveness of adipose tissue to insulin. Moreover, CR significantly decreased the ratio of C/EBPbeta isoforms LAP/LIP, suggesting the suppression of gene transcription associated with terminal differentiation while facilitating preadipocytes proliferation. Morphometric analysis revealed a greater number of small adipocytes in CR relative to AL feeding. Immunostaining confirmed that small adipocytes were more strongly positive for adiponectin than the large ones. Overall these results suggest that CR increased the expression of adipogenic factors, and maintained the differentiated state of adipocytes, which is critically important for adiponectin biosynthesis and insulin sensitivity.  (+info)

Type I and type II fatty acid biosynthesis in Eimeria tenella: enoyl reductase activity and structure. (3/69)

Apicomplexan parasites of the genus Eimeria are the major causative agent of avian coccidiosis, leading to high economic losses in the poultry industry. Recent results show that Eimeria tenella harbours an apicoplast organelle, and that a key biosynthetic enzyme, enoyl reductase, is located in this organelle. In related parasites, enoyl reductase is one component of a type II fatty acid synthase (FAS) and has proven to be an attractive target for antimicrobial compounds. We cloned and expressed the mature form of E. tenella enoyl reductase (EtENR) for biochemical and structural studies. Recombinant EtENR exhibits NADH-dependent enoyl reductase activity and is inhibited by triclosan with an IC50 value of 60 nm. The crystal structure of EtENR reveals overall similarity with other ENR enzymes; however, the active site of EtENR is unoccupied, a state rarely observed in other ENR structures. Furthermore, the position of the central beta-sheet appears to block NADH binding and would require significant movement to allow NADH binding, a feature not previously seen in the ENR family. We analysed the E. tenella genomic database for orthologues of well-characterized bacterial and apicomplexan FAS enzymes and identified 6 additional genes, suggesting that E. tenella contains a type II FAS capable of synthesizing saturated, but not unsaturated, fatty acids. Interestingly, we also identified sequences that appear to encode multifunctional type I FAS enzymes, a feature also observed in Toxoplasma gondii, highlighting the similarity between these apicomplexan parasites.  (+info)

A mammalian type I fatty acid synthase acyl carrier protein domain does not sequester acyl chains. (4/69)

The synthases that produce fatty acids in mammals (FASs) are arranged as large multidomain polypeptides. The growing fatty acid chain is bound covalently during chain elongation and reduction to the acyl carrier protein (ACP) domain that is then able to access each catalytic site. In this work we report the high-resolution nuclear magnetic resonance (NMR) solution structure of the isolated rat fatty acid synthase apoACP domain. The final ensemble of NMR structures and backbone (15)N relaxation studies show that apoACP adopts a single, well defined fold. On conversion to the holo form, several small chemical shift changes are observed on the ACP for residues surrounding the phosphopantetheine attachment site (as monitored by backbone (1)H-(15)N correlation experiments). However, there are negligible chemical shift changes when the holo form is modified to either the hexanoyl or palmitoyl forms. For further NMR analysis, a (13)C,(15)N-labeled hexanoyl-ACP sample was prepared and full chemical shift assignments completed. Analysis of two-dimensional F(2)-filtered and three-dimensional (13)C-edited nuclear Overhauser effect spectroscopy experiments revealed no detectable NOEs to the acyl chain. These experiments demonstrate that unlike other FAS ACPs studied, this Type I ACP does not sequester a covalently linked acyl moiety, although transient interactions cannot be ruled out. This is an important mechanistic difference between the ACPs from Type I and Type II FASs and may be significant for the modulation and regulation of these important mega-synthases.  (+info)

Peroxisome proliferator-activated receptor alpha deficiency abolishes the response of lipogenic gene expression to re-feeding: restoration of the normal response by activation of liver X receptor alpha. (5/69)

The mRNA expression of lipogenic genes Scd-1 and Fas is regulated partly by the insulin-sensitive transcription factor SREBP-1c and liver X receptor alpha (LXRalpha). Compared with normal mice, the increase in the mRNA expression of hepatic Scd-1, Fas, and Srebp-1c was severely attenuated in peroxisome proliferator-activated receptor alpha (PPARalpha)-deficient mice during the transition from the starved to the re-fed states. The concentration of the membrane-bound form of SREBP-1c was also lower in the livers of the PPARalpha-deficient mice during re-feeding but there was little difference in the concentration of the active, nuclear form, or in the abundance of Insig-2a mRNA. The response of plasma insulin to starvation and re-feeding was normal in the PPARalpha-deficient mice. Rat hepatocytes transfected with an adenovirus encoding a dominant negative form of PPARalpha were resistant to the stimulatory effects of insulin on Fas and Scd-1 mRNA expression in vitro. When LXRalpha was activated in vivo by inclusion of a non-steroidal ligand in the diet, the expression of the mRNA for hepatic Srebp-1c, Fas, and Scd-1 was increased severalfold in mice of both genotypes and resistance associated with PPARalpha deficiency was abolished during re-feeding. However, although re-feeding the LXRalpha ligand induced the immature form of SREBP-1c equally in the livers of both genotypes, the concentration of the nuclear form remained relatively low in the livers of the PPARalpha-deficient mice. We conclude that intact PPARalpha is required to mediate the response of Scd-1 and Fas gene expression to insulin and that this is normally achieved directly by activation of LXRalpha.  (+info)

Catalytic residues are shared between two pseudosubunits of the dehydratase domain of the animal fatty acid synthase. (6/69)

Expression, characterization, and mutagenesis of a series of N-terminal fragments of an animal fatty acid synthase, containing the beta-ketoacyl synthase, acyl transferase, and dehydratase domains, demonstrate that the dehydratase domain consists of two pseudosubunits, derived from contiguous regions of the same polypeptide, in which a single active site is formed by the cooperation of the catalytic histidine 878 residue of the first pseudosubunit with aspartate 1032 of the second pseudosubunit. Mutagenesis and modeling studies revealed an essential role for glutamine 1036 in anchoring the position of the catalytic aspartate. These findings establish that sequence elements previously assigned to a central structural core region of the type I fatty acid synthases and some modular polyketide synthase counterparts play an essential catalytic role as part of the dehydratase domain.  (+info)

Direct transfer of starter substrates from type I fatty acid synthase to type III polyketide synthases in phenolic lipid synthesis. (7/69)

 (+info)

Dietary soy protein inhibits DNA damage and cell survival of colon epithelial cells through attenuated expression of fatty acid synthase. (8/69)

 (+info)