Structure and molecular organization of mammalian fatty acid synthase

Asturias, Francisco J.; Chadick, James Z.; Cheung, Iris; Stark, H.; Witkowski, Andrzej; Joshi, Anil K.; Smith, Stuart

doi:10.1038/nsmb899

Cited by 147 publications

(130 citation statements)

References 44 publications

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“…However, secondary structure elements were clearly identifiable, and the electron density map was interpreted by fitting high-resolution structures of individual domain homologues ( Figure 2). The overall X-shape of the FAS structure is very similar to the most recent EM reconstruction (8 ) and, like it, appears asymmetric. As predicted by biochemical and EM analysis (8,9 ), the KS domains are dimeric and, along with the dehydratase (DH) and b-enoyl reductase (ER) domains, form the central portion of the FAS structure.…”

supporting

confidence: 69%

“…The overall X-shape of the FAS structure is very similar to the most recent EM reconstruction (8 ) and, like it, appears asymmetric. As predicted by biochemical and EM analysis (8,9 ), the KS domains are dimeric and, along with the dehydratase (DH) and b-enoyl reductase (ER) domains, form the central portion of the FAS structure. The ER domains are also dimeric (contributing significantly to the monomer-monomer interface), and the DH domains adopt a pseudo-dimeric fold within each monomer.…”

supporting

confidence: 69%

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Mammalian Fatty Acid Synthase: X-ray Structure of a Molecular Assembly Line

Asturias

2006

ACS Chem. Biol.

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F atty acids are ubiquitous cellular components with a variety of structural and metabolic functions, from energy storage to modulation of gene expression. In plants and bacteria, de novo synthesis of fatty acids is carried out by individual enzymes. In contrast, in animal cells, the enzymes involved in fatty acid synthesis are organized in a single fatty acid synthase polypeptide (Figure 1). Encompassing all of the activities required to retain and extend an acyl chain from acetyl-CoA and malonyl-CoA precursors and then release a full-length, long-chain fatty acid, mammalian fatty acid synthase (FAS) constitutes a true molecular assembly line (1 ). Human FAS is a target for drug development against obesity and related diseases, and FAS inhibitors have been shown to have antitumor activity. Although the biochemistry of fatty acid synthesis was established over 30 years ago, structural understanding of FAS had, until recently, been limited (high-resolution structures of individual prokaryotic enzymes and a couple of FAS domains were available). The situation has changed dramatically with the recent publication of the first X-ray structure of FAS by Nenad Ban and colleagues (2 ).In mammalian cells, the functional form of FAS is a homodimer (MW ~540 000 Da) with two centers for fatty acid synthesis. The model for FAS organization that prevailed for over 20 years was based on a logical but naïve interpretation of the possible structure of an FAS monomer (3 ). It was observed that the bifunctional compound dibromopropanone could cross-link the thiol in the active site cysteine of the N-terminal b-ketoacyl synthase (KS) domain of one monomer with the thiol in the phosphopantetheine group of the acyl carrier protein (ACP) located near the C-terminus of the other monomer. Therefore, a model with two extended FAS monomers in an antiparallel arrangement was proposed, thereby providing a simple explanation for the complementary interaction of the N-terminal condensing domains of one monomer with the C-terminal reducing and chain terminating domains of the other. However, functional complementation studies of baculovirusexpressed active site FAS mutants revealed a number of intramonomer interactions that could not be explained by the extended, antiparallel model of FAS (4 ). Careful re-examination of the dibromopropanone experiment (5 ) also revealed both intra-and intermonomer cross-links. These investigations eventually resulted in the formulation of an alternative model for FAS organization in which the two monomers were intertwined (6 ) (Box 1).The paucity of structural information on FAS that prevailed until very recently illustrates some of the challenges in structural analysis of large macromolecular complexes. A relatively new technique that can often be used to determine low (10-30 Å)-resolution structures of large macromolecules is molecular electron microscopy (EM). Analysis of FAS by EM was complicated by the flexibility of the molecule, and a first low-resolution 3-D EM reconstruction of FAS was interpreted A B...

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supporting

confidence: 69%

supporting

confidence: 69%

Mammalian Fatty Acid Synthase: X-ray Structure of a Molecular Assembly Line

Asturias

2006

ACS Chem. Biol.

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“…The primary fungal FAS subunits are homologous to HexA (Ϸ53% similarity, global alignment) and HexB (Ϸ52% similarity); however, binding to PksA induces a proposed ␣ 2 ␤ 2 ␥ 2 arrangement, quite distinct from the ␣ 6 ␤ 6 organization observed for yeast FAS. On the other hand, mammalian FAS associates as an ␣ 2 head-to-head homodimer with centrally located KS domains, as demonstrated for modular PKSs and hypothesized for PksA (12,30). The unique ␣ 2 ␤ 2 ␥ 2 oligomerization state of NorS must place the SAT domain in a location accessible to both the ACP domain of HexA and the ACP in PksA for efficient transfer and catalysis.…”

Section: Discussionmentioning

confidence: 99%

Identification of a starter unit acyl-carrier protein transacylase domain in an iterative type I polyketide synthase

Crawford

Dancy

Hill

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

165

184

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Polyketides are a class of natural products that exhibit a wide range of functional and structural diversity. They include antibiotics, immunosuppressants, antifungals, antihypercholesterolemics, and cytotoxins. Polyketide synthases (PKSs) use chemistry similar to fatty acid synthases (FASs), although building block variation and differing extents of reduction of the growing polyketide chain underlie their biosynthetic versatility. In contrast to the well studied sequential modular type I PKSs, less is known about how the iterative type I PKSs carry out and control chain initiation, elongation, folding, and cyclization during polyketide processing. Domain structure analysis of a group of related fungal, nonreducing PKSs has revealed well defined N-terminal domains longer than commonly seen for FASs and modular PKSs. Predicted structure of this domain disclosed a region similar to malonyl-CoA:acyl-carrier protein (ACP) transacylases (MATs). MATs play a key role transferring precursor CoA thioesters from solution onto FASs and PKSs for chain elongation. On the basis of site-directed mutagenesis, radiolabeling, and kinetics experiments carried out with individual domains of the norsolorinic acid PKS, we propose that the Nterminal domain is a starter unit:ACP transacylase (SAT domain) that selects a C6 fatty acid from a dedicated yeast-like FAS and transfers this unit onto the PKS ACP, leading to the production of the aflatoxin precursor, norsolorinic acid. These findings could indicate a much broader role for SAT domains in starter unit selection among nonreducing iterative, fungal PKSs, and they provide a biochemical rationale for the classical acetyl ''starter unit effect.'' aflatoxin biosynthesis ͉ fatty acid synthase

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“…S1). Mammalian FAS has been studied by cryoelectron microscopy (cryo-EM) (4,5) and x-ray crystallography (6) and was found to be a highly flexible complex (7). The mobile acyl carrier protein (ACP) domain has not yet been directly observed in the mammalian FAS system.…”

mentioning

confidence: 99%

Direct structural insight into the substrate-shuttling mechanism of yeast fatty acid synthase by electron cryomicroscopy

Gipson

Mills

Wouts

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

126

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Yeast fatty acid synthase (FAS) is a 2.6-MDa barrel-shaped multienzyme complex, which carries out cyclic synthesis of fatty acids. By electron cryomicroscopy of single particles we obtained a threedimensional map of yeast FAS at 5.9-Å resolution. Compared to the crystal structures of fungal FAS, the EM map reveals major differences and new features that indicate a considerably different arrangement of the complex in solution compared to the crystal structures, as well as a high degree of variance inside the barrel. Distinct density regions in the reaction chambers next to each of the catalytic domains fitted the substrate-binding acyl carrier protein (ACP) domain. In each case, this resulted in the expected distance of ∼18 Å from the ACP substrate-binding site to the active site of the catalytic domains. The multiple, partially occupied positions of the ACP within the reaction chamber provide direct structural insight into the substrate-shuttling mechanism of fatty acid synthesis in this large cellular machine.cryoelectron microscopy | fatty acid synthesis | acyl carrier protein | molecular architecture

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Structure and molecular organization of mammalian fatty acid synthase

Cited by 147 publications

References 44 publications

Mammalian Fatty Acid Synthase: X-ray Structure of a Molecular Assembly Line

Mammalian Fatty Acid Synthase: X-ray Structure of a Molecular Assembly Line

Identification of a starter unit acyl-carrier protein transacylase domain in an iterative type I polyketide synthase

Direct structural insight into the substrate-shuttling mechanism of yeast fatty acid synthase by electron cryomicroscopy

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