Cholesteryl ester transfer protein (CETP) shuttles various lipids between lipoproteins, resulting in the net transfer of cholesteryl esters from atheroprotective, high-density lipoproteins (HDL) to atherogenic, lower-density species. Inhibition of CETP raises HDL cholesterol and may potentially be used to treat cardiovascular disease. Here we describe the structure of CETP at 2.2-A resolution, revealing a 60-A-long tunnel filled with two hydrophobic cholesteryl esters and plugged by an amphiphilic phosphatidylcholine at each end. The two tunnel openings are large enough to allow lipid access, which is aided by a flexible helix and possibly also by a mobile flap. The curvature of the concave surface of CETP matches the radius of curvature of HDL particles, and potential conformational changes may occur to accommodate larger lipoprotein particles. Point mutations blocking the middle of the tunnel abolish lipid-transfer activities, suggesting that neutral lipids pass through this continuous tunnel.
Squalene synthase catalyzes the biosynthesis of squalene, a key cholesterol precursor, through a reductive dimerization of two farnesyl diphosphate (FPP) molecules. The reaction is unique when compared with those of other FPP-utilizing enzymes and proceeds in two distinct steps, both of which involve the formation of carbocationic reaction intermediates. Because FPP is located at the final branch point in the isoprenoid biosynthesis pathway, its conversion to squalene through the action of squalene synthase represents the first committed step in the formation of cholesterol, making it an attractive target for therapeutic intervention. We have determined, for the first time, the crystal structures of recombinant human squalene synthase complexed with several different inhibitors. The structure shows that SQS is folded as a single domain, with a large channel in the middle of one face. The active sites of the two half-reactions catalyzed by the enzyme are located in the central channel, which is lined on both sides by conserved aspartate and arginine residues, which are known from mutagenesis experiments to be involved in FPP binding. One end of this channel is exposed to solvent, whereas the other end leads to a completely enclosed pocket surrounded by conserved hydrophobic residues. These observations, along with mutagenesis data identifying residues that affect substrate binding and activity, suggest that two molecules of FPP bind at one end of the channel, where the active center of the first half-reaction is located, and then the stable reaction intermediate moves into the deep pocket, where it is sequestered from solvent and the second half-reaction occurs. Five ␣ helices surrounding the active center are structurally homologous to the active core in the three other isoprenoid biosynthetic enzymes whose crystal structures are known, even though there is no detectable sequence homology.The isoprenoid biosynthetic pathway yields a structurally diverse family of low molecular weight molecules with a variety of physiological functions (1-3). In humans, the pathway produces such critical end-products as cholesterol, bile acids, dolichol, ubiquinone, steroid hormones, and prenylated proteins. Chain length-selective prenyltransferases catalyze the successive head-to-tail addition of the 5-carbon (C5-) isopentenyl diphosphate to the growing isoprene chain to form a series of linear C10-, C15-, C20-and C25-isoprenoid diphosphates. Cyclic terpenes are formed from these linear isoprenoid diphosphates through the actions of numerous class I terpene cyclases (3). The longer 30-carbon linear terpene, squalene, of cholesterol biosynthesis and the 40-carbon linear terpene, phytoene, of carotenoid biosynthesis are formed by head-to-head condensations, respectively, of two 15-carbon and 20-carbon isoprenoid diphosphates, through the actions of the prenyltransferases squalene synthase and phytoene synthase (4) and are subsequently converted into their respective cyclic terpenes through the action of specific class II terpene c...
N-Aryl pyrazoles were prepared from anilines in a three step telescoped approach. An aniline was diazotized to give the diazonium fluoroborate, followed by reduction with tin(II) chloride to give the corresponding hydrazine, which in turn reacted with a ketoenamine to give the N-aryl pyrazole. The deprotection of the methyl ether was accomplished with PhBCl 2 to give the final product. The continuous flow methodology was used to minimize accumulation of the highly energetic and potentially explosive diazonium salt and hydrazine intermediates to enable the safe scale-up of N-aryl pyrazoles. The heterogeneous reaction mixture was successfully handled in both lab scale and production scale. A continuous extraction was employed to remove organic impurities from the diazotization step, which eliminated the need for chromatography in the purification of the final N-aryl pyrazole.
Peroxisomal proliferator-activated receptor (PPAR)-␣ is a ligand-activated transcriptional factor that regulates genes involved in lipid metabolism and energy homeostasis. PPAR-␣ activators, including fibrates, have been used to treat dyslipidemia for several decades. In contrast to their known effects on lipids, the pharmacological consequences of PPAR-␣ activation on cardiac metabolism and function are not well understood. Therefore, we evaluated the role that PPAR-␣ receptors play in the heart. Our studies demonstrate that activation of PPAR-␣ receptors using a selective PPAR-␣ ligand results in cardiomyocyte necrosis in mice. Studies in PPAR-␣-deficient mice demonstrated that cardiomyocyte necrosis is a consequence of the activation of PPAR-␣ receptors. Cardiac fatty acyl-CoA oxidase mRNA levels increased at doses in which cardiac damage was observed and temporally preceded cardiomyocyte degeneration, suggesting that peroxisomal -oxidation correlates with the appearance of microscopic injury and cardiac injury biomarkers. Increased myocardial oxidative stress was evident in mice treated with the PPAR-␣ agonists coinciding with increased peroxisomal biomarkers of fatty acid oxidation. These findings suggest that activation of PPAR-␣ leads to increased cardiac fatty acid oxidation and subsequent accumulation of oxidative stress intermediates resulting in cardiomyocyte necrosis. (Am J
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.