Comparison of the backbone dynamics of the apo- and holo-carboxy-terminal domain of the biotin carboxyl carrier subunit of Escherichia coli acetyl-CoA carboxylase.
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The biotin carboxyl carrier protein (BCCP) is a subunit of acetyl-CoA carboxylase, a biotin-dependent enzyme that catalyzes the first committed step of fatty acid biosynthesis. In its functional cycle, this protein engages in heterologous protein-protein interactions with three distinct partners, depending on its state of post-translational modification. Apo-BCCP interacts specifically with the biotin holoenzyme synthetase, BirA, which results in the post-translational attachment of biotin to a single lysine residue on BCCP. Holo-BCCP then interacts with the biotin carboxylase subunit of acetyl-CoA carboxylase, which leads to the addition of the carboxylate group of bicarbonate to biotin. Finally, the carboxy-biotinylated form of BCCP interacts with transcarboxylase in the transfer of the carboxylate to acetyl-CoA to form malonyl-CoA. The determinants of protein-protein interaction specificity in this system are unknown. The NMR solution structure of the unbiotinylated form of an 87 residue C-terminal domain fragment (residue 70-156) of BCCP (holoBCCP87) and the crystal structure of the biotinylated form of a C-terminal fragment (residue 77-156) of BCCP from Escherichia coli acetyl-CoA carboxylase have previously been determined. Comparative analysis of these structures provided evidence for small, localized conformational changes in the biotin-binding region upon biotinylation of the protein. These structural changes may be important for regulating specific protein-protein interactions. Since the dynamic properties of proteins are correlated with local structural environments, we have determined the relaxation parameters of the backbone 15N nuclear spins of holoBCCP87, and compared these with the data obtained for the apo protein. The results indicate that upon biotinylation, the inherent mobility of the biotin-binding region and the protruding thumb, with which the biotin group interacts in the holo protein, are significantly reduced. (+info)
A multisubunit acetyl coenzyme A carboxylase from soybean.
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A multisubunit form of acetyl coenzyme A (CoA) carboxylase (ACCase) from soybean (Glycine max) was characterized. The enzyme catalyzes the formation of malonyl CoA from acetyl CoA, a rate-limiting step in fatty acid biosynthesis. The four known components that constitute plastid ACCase are biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and the alpha- and beta-subunits of carboxyltransferase (alpha- and beta-CT). At least three different cDNAs were isolated from germinating soybean seeds that encode BC, two that encode BCCP, and four that encode alpha-CT. Whereas BC, BCCP, and alpha-CT are products of nuclear genes, the DNA that encodes soybean beta-CT is located in chloroplasts. Translation products from cDNAs for BC, BCCP, and alpha-CT were imported into isolated pea (Pisum sativum) chloroplasts and became integrated into ACCase. Edman microsequence analysis of the subunits after import permitted the identification of the amino-terminal sequence of the mature protein after removal of the transit sequences. Antibodies specific for each of the chloroplast ACCase subunits were generated against products from the cDNAs expressed in bacteria. The antibodies permitted components of ACCase to be followed during fractionation of the chloroplast stroma. Even in the presence of 0.5 M KCl, a complex that contained BC plus BCCP emerged from Sephacryl 400 with an apparent molecular mass greater than about 800 kD. A second complex, which contained alpha- and beta-CT, was also recovered from the column, and it had an apparent molecular mass of greater than about 600 kD. By mixing the two complexes together at appropriate ratios, ACCase enzymatic activity was restored. Even higher ACCase activities were recovered by mixing complexes from pea and soybean. The results demonstrate that the active form of ACCase can be reassembled and that it could form a high-molecular-mass complex. (+info)
The Saccharomyces cerevisiae hyperrecombination mutant hpr1Delta is synthetically lethal with two conditional alleles of the acetyl coenzyme A carboxylase gene and causes a defect in nuclear export of polyadenylated RNA.
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In a screen for mutants that display synthetic lethal interaction with hpr1Delta, a hyperrecombination mutant of Saccharomyces cerevisiae, we have isolated a novel cold-sensitive allele of the acetyl coenzyme A (CoA) carboxylase gene, acc1(cs), encoding the rate-limiting enzyme of fatty acid synthesis. The synthetic lethal phenotype of the acc1(cs) hpr1Delta double mutant was only partially complemented by exogenous fatty acids. hpr1Delta was also synthetically lethal with a previously isolated, temperature-sensitive allele of ACC1, mtr7 (mRNA transport), indicating that the lethality of the acc1(cs) hpr1Delta double mutant was not allele specific. The basis for the interaction between conditional acc1 alleles and hpr1Delta was investigated in more detail. In the hpr1Delta mutant background, acetyl-CoA carboxylase enzyme activity was reduced about 15-fold and steady-state levels of biotinylated Acc1p and ACC1 mRNA were reduced 2-fold. The reduced Acc1p activity in hpr1Delta cells, however, did not result in an altered lipid or fatty acid composition of the mutant membranes but rendered cells hypersensitive to soraphen A, an inhibitor of Acc1p. Similar to mtr7, hpr1Delta and acc1(cs) mutant cells displayed a defect in nuclear export of polyadenylated RNA. Oversized transcripts were detected in hpr1Delta, and rRNA processing was disturbed, but pre-mRNA splicing appeared wild type. Surprisingly, the transport defect of hpr1Delta and acc1(cs) mutant cells was accompanied by an altered ring-shaped structure of the nucleolus. These observations suggest that the basis for the synthetic lethal interaction between hpr1Delta and acc1 may lie in a functional overlap of the two mutations in nuclear poly(A)+ RNA production and export that results in an altered structure of the nucleolus. (+info)
Light-dependent changes in redox status of the plastidic acetyl-CoA carboxylase and its regulatory component.
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Plastidic acetyl-CoA carboxylase (ACCase; EC 6.4.1.2), which catalyses the synthesis of malonyl-CoA and is the regulatory enzyme of fatty acid synthesis, is activated by light, presumably under redox regulation. To obtain evidence of redox regulation in vivo, the activity of ACCase was examined in pea chloroplasts isolated from plants kept in darkness (dark-ACCase) or after exposure to light for 1 h (light-ACCase) in the presence or absence of a thiol-reducing agent, dithiothreitol (DTT). The protein level was similar for light-ACCase and dark-ACCase, but the activity of light-ACCase in the absence of DTT was approx. 3-fold that of dark-ACCase. The light-ACCase and dark-ACCase were activated approx. 2-fold and 6-fold by DTT respectively, indicating that light-ACCase was in a much more reduced, active form than the dark-ACCase. This is the first demonstration of the light-dependent reduction of ACCase in vivo. Measurement of the activities of ACCase, carboxyltransferase and biotin carboxylase in the presence and absence of DTT, and the thiol-oxidizing agent, 5, 5'-dithiobis-(2-nitrobenzoic) acid, revealed that the carboxyltransferase reaction, but not the biotin carboxylase reaction, was redox-regulated. The cysteine residue(s) responsible for redox regulation probably reside on the carboxyltransferase component. Measurement of the pH dependence of biotin carboxylase and carboxyltransferase activities in the ACCase suggested that both components affect the activity of ACCase in vivo at a physiological pH range. These results suggest that the activation of ACCase by light is caused partly by the pH-dependent activation of two components and by the reductive activation of carboxyltransferase. (+info)
Phosphorylation control of cardiac acetyl-CoA carboxylase by cAMP-dependent protein kinase and 5'-AMP activated protein kinase.
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Acetyl-CoA carboxylase (ACC) is regarded in liver and adipose tissue to be the rate-limiting enzyme for fatty acid biosynthesis; however, in heart tissue it functions as a regulator of fatty acid oxidation. Because the control of fatty acid oxidation is important to the functioning myocardium, the regulation of ACC is a key issue. Two cardiac isoforms of ACC exist, with molecular masses of 265 kDa and 280 kDa (ACC265 and ACC280). In this study, these proteins were purified from rat heart and used in subsequent phosphorylation and immunoprecipitation experiments. Our results demonstrate that 5' AMP-activated protein kinase (AMPK) is able to phosphorylate both ACC265 and ACC280, resulting in an almost complete loss of ACC activity. Although cAMP-dependent protein kinase phosphorylated only ACC280, a dramatic loss of ACC activity was still observed, suggesting that ACC280 contributes most, if not all, of the total heart ACC activity. ACC280 and ACC265 copurified under all experimental conditions, and purification of heart ACC also resulted in the specific copurification of the alpha2 isoform of the catalytic subunit of AMPK. Although both catalytic subunits of AMPK were expressed in crude heart homogenates, our results suggest that alpha2, and not alpha1, is the dominant isoform of AMPK catalytic subunit regulating ACC in the heart. Immunoprecipitation studies demonstrated that specific antibodies for both ACC265 and ACC280 were able to coimmunoprecipitate the alternate isoform along with the alpha2 isoform of AMPK. Taken together, the immunoprecipitation and the purification studies suggest that the two isoforms of ACC in the heart exist in a heterodimeric structure, and that this structure is tightly associated with the alpha2 subunit of AMPK. (+info)
Induction of lipogenesis during differentiation in a "preadipocyte" cell line.
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3T3-L1 fibroblasts differentiate in culture into cells having adipocyte character. This transition is accompanied by a 40- to 50-fold rise in the incorporation of [14C]acetate into triglyceride. The increase in lipogenic rate is exactly parallel to a coordinate rise in the activities of the key enzymes of the fatty acid biosynthetic pathway (ATP-citrate lyase, acetyl-CoA carboxylase, and fatty acid synthetase). Immunological studies indicate that the elevated acetyl-CoA carboxylase activity is the product of an increased cellular enzyme level. (+info)
Structure and selectivity in post-translational modification: attaching the biotinyl-lysine and lipoyl-lysine swinging arms in multifunctional enzymes.
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The post-translational attachment of biotin and lipoic acid to specific lysine residues displayed in protruding beta-turns in homologous biotinyl and lipoyl domains of their parent enzymes is catalysed by two different ligases. We have expressed in Escherichia coli a sub-gene encoding the biotinyl domain of E.coli acetyl-CoA carboxylase, and by a series of mutations converted the protein from the target for biotinylation to one for lipoylation, in vivo and in vitro. The biotinylating enzyme, biotinyl protein ligase (BPL), and the lipoylating enzyme, LplA, exhibited major differences in the recognition process. LplA accepted the highly conserved MKM motif that houses the target lysine residue in the biotinyl domain beta-turn, but was responsive to structural cues in the flanking beta-strands. BPL was much less sensitive to changes in these beta-strands, but could not biotinylate a lysine residue placed in the DKA motif characteristic of the lipoyl domain beta-turn. The presence of a further protruding thumb between the beta2 and beta3 strands in the wild-type biotinyl domain, which has no counterpart in the lipoyl domain, is sufficient to prevent aberrant lipoylation in E.coli. The structural basis of this discrimination contrasts with other forms of post-translational modification, where the sequence motif surrounding the target residue can be the principal determinant. (+info)
Volume overload hypertrophy of the newborn heart slows the maturation of enzymes involved in the regulation of fatty acid metabolism.
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OBJECTIVES: The purpose of this study was to determine the effect of volume overload hypertrophy in the newborn heart on the cardiac enzymes controlling fatty acid metabolism. BACKGROUND: Shortly after birth, a rise in 5'-adenosine monophosphate-activated protein kinase (AMPK) activity results in the phosphorylation and inhibition of acetyl coenzyme A (CoA) carboxylase (ACC), and a decline in myocardial malonyl CoA levels with increased fatty acid oxidation rates. Whether the early onset of hypertrophy in the newborn heart alters this maturational increase in fatty acid oxidation is unknown. METHODS: Newborn piglets underwent endovascular stenting of the ductus arteriosus on day 1 of life with a 4.5-mm diameter stent, resulting in a left to right shunt, and left ventricular (LV) volume loading. Left ventricular and right ventricular samples from fetal, newborn, three-week control and three-week stented animals were compared. RESULTS: Stenting resulted in echocardiographic evidence of volume overload and myocardial hypertrophy. In control animals, left ventricular ACC activity declined from 274 +/- 30 pmol/mg/min on day 1 to 115 +/- 12 after three weeks (p < 0.05), but did not display this maturation drop in hypertrophied hearts, remaining elevated (270 +/- 50 pmol/mg/min, p < 0.05). At three weeks, malonyl CoA levels remained 2.8-fold higher in hypertrophied hearts than in control hearts. In control hearts, LV AMPK activity increased 178% between day 1 and three weeks, whereas in hypertrophied hearts AMPK activity at three weeks was only 71% of control values, due to a significant decrease in expression of the catalytic subunit of AMPK. CONCLUSIONS: Early onset LV volume overload with hypertrophy results in a delay in the normal maturation of fatty acid oxidation in the newborn heart. (+info)