Structure of the human beta-ketoacyl [ACP] synthase from the mitochondrial type II fatty acid synthase

Modular polyketide synthase ketosynthases collaborate with upstream dehydratases to install double bonds

A VMYH motif was determined to help ketosynthases in polyketide assembly lines select α,β-unsaturated intermediates from an equilibrium mediated by an upstream dehydratase. Alterations of this motif decreased ketosynthase selectivity within a model tetraketide synthase, most significantly when replaced by the TNGQ motif of ketosynthases that accept D-β-hydroxy intermediates.

Assessing and harnessing updated polyketide synthase modules through combinatorial engineering

The modular nature of polyketide assembly lines and the significance of their products make them prime targets for combinatorial engineering. The recently updated module boundary has been successful for engineering short synthases, yet larger synthases constructed using the updated boundary have not been investigated. Here we describe our design and implementation of a BioBricks-like platform to rapidly construct 5 triketide, 25 tetraketide, and 125 pentaketide synthases to test every module combination of the pikromycin synthase. Anticipated products are detected from 60% of the triketide synthases, 32% of the tetraketide synthases, and 6.4% of the pentaketide synthases. We determine ketosynthase gatekeeping and module-skipping are the principal impediments to obtaining functional synthases. The platform is also employed to construct active hybrid synthases by incorporating modules from the erythromycin, spinosyn, and rapamycin assembly lines. The relaxed gatekeeping of a ketosynthase in the rapamycin synthase is especially encouraging in the quest to produce designer polyketides.

Substrate Sequestration and Chain Flipping in Human Mitochondrial Acyl Carrier Protein

Outside of their involvement in energy production, mitochondria play a critical role for the cell through their access to a discrete pathway for fatty acid biosynthesis. Despite decades of study in bacterial fatty acid synthases (the putative evolutionary mitochondrial precursor), our understanding of human mitochondrial fatty acid biosynthesis remains incomplete. In particular, the role of the key carrier protein, human mitochondrial acyl carrier protein (mACP), which shuttles the substrate intermediates through the pathway, has not been well-studied in part due to challenges in protein expression and purification. Herein, we report a reliable method for recombinant Escherichia coli expression and purification of mACP. Fundamental characteristics, including substrate sequestration and chain-flipping activity, are demonstrated in mACP using solvatochromic response. This study provides an efficient approach toward understanding the fundamental protein-protein interactions of mACP and its partner proteins, ultimately leading to a molecular understanding of human mitochondrial diseases such as mitochondrial fatty acid oxidation deficiencies.

Diarylpentanoids, the privileged scaffolds in antimalarial and anti-infectives drug discovery: A review

Asia is a hotspot for infectious diseases, including malaria, dengue fever, tuberculosis, and the pandemic COVID-19. Emerging infectious diseases have taken a heavy toll on public health and the economy and have been recognized as a major cause of morbidity and mortality, particularly in Southeast Asia. Infectious disease control is a major challenge, but many surveillance systems and control strategies have been developed and implemented. These include vector control, combination therapies, vaccine development, and the development of new anti-infectives. Numerous newly discovered agents with pharmacological anti-infective potential are being actively and extensively studied for their bioactivity, toxicity, selectivity, and mode of action, but many molecules lose their efficacy over time due to resistance developments. These facts justify the great importance of the search for new, effective, and safe anti-infectives. Diarylpentanoids, a curcumin derivative, have been developed as an alternative with better bioavailability and metabolism as a therapeutic agent. In this review, the mechanisms of action and potential targets of antimalarial drugs as well as the classes of antimalarial drugs are presented. The bioactivity of diarylpentanoids as a potential scaffold for a new class of anti-infectives and their structure-activity relationships are also discussed in detail.

Assessing and harnessing updated polyketide synthase modules through combinatorial engineering

The modular nature of polyketide assembly lines and the significance of their products make them prime targets for combinatorial engineering. While short synthases constructed using the recently updated module boundary have been shown to outperform those using the traditional boundary, larger synthases constructed using the updated boundary have not been investigated. Here we describe our design and implementation of a BioBricks-like platform to rapidly construct 5 triketide, 25 tetraketide, and 125 pentaketide synthases from the updated modules of the Pikromycin synthase. Every combinatorial possibility of modules 2-6 inserted between the first and last modules of the native synthase was constructed and assayed. Anticipated products were observed from 60% of the triketide synthases, 32% of the tetraketide synthases, and 6.4% of the pentaketide synthases. Ketosynthase gatekeeping and module-skipping were determined to be the principal impediments to obtaining functional synthases. The platform was also used to create functional hybrid synthases through the incorporation of modules from the Erythromycin, Spinosyn, and Rapamycin assembly lines. The relaxed gatekeeping observed from a ketosynthase in the Rapamycin synthase is especially encouraging in the quest to produce designer polyketides.

Enzymology of standalone elongating ketosynthases

The β-ketoacyl-acyl carrier protein synthase, or ketosynthase (KS), catalyses carbon-carbon bond formation in fatty acid and polyketide biosynthesis via a decarboxylative Claisen-like condensation. In prokaryotes, standalone elongating KSs interact with the acyl carrier protein (ACP) which shuttles substrates to each partner enzyme in the elongation cycle for catalysis. Despite ongoing research for more than 50 years since KS was first identified in E. coli, the complex mechanism of KSs continues to be unravelled, including recent understanding of gating motifs, KS-ACP interactions, substrate recognition and delivery, and roles in unsaturated fatty acid biosynthesis. In this review, we summarize the latest studies, primarily conducted through structural biology and molecular probe design, that shed light on the emerging enzymology of standalone elongating KSs.

How cis-Acyltransferase Assembly-Line Ketosynthases Gatekeep for Processed Polyketide Intermediates

With the redefinition of polyketide synthase (PKS) modules, a new appreciation of their most downstream domain, the ketosynthase (KS), is emerging. In addition to performing its well-established role of generating a carbon-carbon bond between an acyl-CoA building block and a growing polyketide, it may gatekeep against incompletely processed intermediates. Here, we investigate 739 KSs from 92 primarily actinomycete, cis-acyltransferase assembly lines. When KSs were separated into 16 families based on the chemistries at the α- and β-carbons of their polyketide substrates, a comparison of 32 substrate tunnel residues revealed unique sequence fingerprints. Surprisingly, additional fingerprints were detected when the chemistry at the γ-carbon was considered. Representative KSs were modeled bound to their natural polyketide substrates to better understand observed patterns, such as the substitution of a tryptophan by a smaller residue to accommodate an l-α-methyl group or the substitution of four smaller residues by larger ones to make better contact with a primer unit or diketide. Mutagenesis of a conserved glutamine in a KS within a model triketide synthase indicates that the substrate tunnel is sensitive to alteration and that engineering this KS to accept unnatural substrates may require several mutations.

Animal Fatty Acid Synthase: A Chemical Nanofactory

Fatty acids are crucial molecules for most living beings, very well spread and conserved across species. These molecules play a role in energy storage, cell membrane architecture, and cell signaling, the latter through their derivative metabolites. De novo synthesis of fatty acids is a complex chemical process that can be achieved either by a metabolic pathway built by a sequence of individual enzymes, such as in most bacteria, or by a single, large multi-enzyme, which incorporates all the chemical capabilities of the metabolic pathway, such as in animals and fungi, and in some bacteria. Here we focus on the multi-enzymes, specifically in the animal fatty acid synthase (FAS). We start by providing a historical overview of this vast field of research. We follow by describing the extraordinary architecture of animal FAS, a homodimeric multi-enzyme with seven different active sites per dimer, including a carrier protein that carries the intermediates from one active site to the next. We then delve into this multi-enzyme's detailed chemistry and critically discuss the current knowledge on the chemical mechanism of each of the steps necessary to synthesize a single fatty acid molecule with atomic detail. In line with this, we discuss the potential and achieved FAS applications in biotechnology, as biosynthetic machines, and compare them with their homologous polyketide synthases, which are also finding wide applications in the same field. Finally, we discuss some open questions on the architecture of FAS, such as their peculiar substrate-shuttling arm, and describe possible reasons for the emergence of large megasynthases during evolution, questions that have fascinated biochemists from long ago but are still far from answered and understood.

Virtual screening-based identification of novel fatty acid synthase inhibitor and evaluation of its antiproliferative activity in breast cancer cells

Cancer cells activate de novo lipogenesis by overexpressing the lipogenic enzymes ACLY, ACC and FASN to support rapid cell division. FASN, previously known as oncogenic antigen-519 (OA-519) catalyzes seven sequential reactions to synthesize palmitic acid (C16) from substrates acetyl CoA, and malonyl CoA. The dependence of cancer cells on FASN-derived lipids and the differential expression of FASN in cancer cells compared to their normal counterparts make it an attractive metabolic drug target in cancer therapy. In the present study, an attempt has been made to identify potent FASN inhibitors from Asinex-Synergy compound database using structure-based virtual screening. The serial docking protocols of increasing precisions identified LEG-17649942, with glide score -10.34 kcal/mol as a promising compound which can directly interact with active site residues H293 and H331. LEG-17649942 possesses drug-like pharmacokinetic properties as predicted by Qikprop. LEG-17649942 exhibited cytotoxicity in breast cancer cell lines SK-BR-3, MCF-7 and MDA-MB-231 with maximum activity against MDA-MB-231 cells with IC50 of 50 μM. The study put forward LEG-17649942 as a novel drug-lead compound against triple negative breast cancer with an exquisite binding pattern to FASN-KS domain.

Novel Targets for Antimicrobials

Antimicrobial resistance (AMR) is the phenomenon developed by microorganism on exposure to antimicrobial agents, making them unresponsive. Development of microbial confrontation is a severe rising risk to global community well-being as treatment in addition, management of such resistant microbial infections is difficult and challenging. The situation requires action across all government sectors and society. The change in the molecular target on which antimicrobial drugs act is one of the key mechanisms behind AMR. One of the approaches to battle with AMR can be exploring newer molecular targets in microbes and discovering new molecules accordingly. There are various examples of novel targets such as biomolecules involving in biosynthesis of cell wall, biosynthesis of aromatic amino acid, cell disunion, biosynthesis of fatty acid, and isoprenoid biosynthesis and tRNA synthetases. Fatty acid biosynthesis (FAB) and their enzymes among all the above is the more appealing target for the advancement of new antimicrobial agents. Number of promising inhibitors have been developed for bacterial fatty acid synthesis (FAS) and also few of them are clinically used. Some of these potential inhibitors are found to be used in development of new antibacterial as a lead compound and have been discovered from high throughput screening processes like Platencimycin and their analogue, Platencin. The review majorly encompasses bacterial FAB in type II FAS system and potential inhibitors with respective targets of novel antibacterial.

A mass spectrometry-based high-throughput screening method for engineering fatty acid synthases with improved production of medium-chain fatty acids

Microbial cell factories have been extensively engineered to produce free fatty acids (FFAs) as key components of crucial nutrients, soaps, industrial chemicals, and fuels. However, our ability to control the composition of microbially synthesized FFAs is still limited, particularly, for producing medium-chain fatty acids (MCFAs). This is mainly due to the lack of high-throughput approaches for FFA analysis to engineer enzymes with desirable product specificity. Here we report a mass spectrometry (MS)-based method for rapid profiling of MCFAs in Saccharomyces cerevisiae by using membrane lipids as a proxy. In particular, matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) MS was used to detect shorter acyl chain phosphatidylcholines from membrane lipids and a higher m/z peak ratio at 730 and 758 was used as an indication for improved MCFA production. This colony-based method can be performed at a rate of ~2 s per sample, representing a substantial improvement over gas chromatography-MS (typically >30 min per sample) as the gold standard method for FFA detection. To demonstrate the power of this method, we performed site-saturation mutagenesis of the yeast fatty acid synthase and identified nine missense mutations that resulted in improved MCFA production relative to the wild-type strain. Colony-based MALDI-ToF MS screening provides an effective approach for engineering microbial fatty acid compositions in a high-throughput manner.

Fluorine-Containing Chrysin Derivatives

Chrysin, a flavonoid, has played a great role in the fields of anticancer, antibacterial, and antiviral drug discovery. A large number of chrysin derivatives have been synthesized recently. The fluorine atom represents an important substituent group for a great number of natural products and pharmaceuticals. Taking into account the importance of both chrysin and the fluorine atom in medicinal chemistry, the synthesis of fluorine-containing chrysin derivatives has gained great interest. Chemically, the synthetic methods for these new chrysin derivatives have also been developed rapidly. In recent years, research on their synthesis has been focused on speeding up the reaction process by changing the catalyst. Biologically, the purpose of introducing fluorine into chrysin was to improve its lipophilicity, but today it is mainly focused on the enhancement and improvement of either its anticancer or antimicrobial activities by incorporating the special properties of fluorine atoms. In this review, synthetic methods for the introduction of fluorine atoms into chrysin are summarized, and their anticancer, antibacterial, antiviral, and hypoglycemic effects are discussed.

Mitochondrial acyl carrier protein (ACP) at the interface of metabolic state sensing and mitochondrial function

Acyl carrier protein (ACP) is a principal partner in the cytosolic and mitochondrial fatty acid synthesis (FAS) pathways. The active form holo-ACP serves as FAS platform, using its 4'-phosphopantetheine group to present covalently attached FAS intermediates to the enzymes responsible for the acyl chain elongation process. Mitochondrial unacylated holo-ACP is a component of mammalian mitoribosomes, and acylated ACP species participate as interaction partners in several ACP-LYRM (leucine-tyrosine-arginine motif)-protein heterodimers that act either as assembly factors or subunits of the electron transport chain and Fe-S cluster assembly complexes. Moreover, octanoyl-ACP provides the C8 backbone for endogenous lipoic acid synthesis. Accumulating evidence suggests that mtFAS-generated acyl-ACPs act as signaling molecules in an intramitochondrial metabolic state sensing circuit, coordinating mitochondrial acetyl-CoA levels with mitochondrial respiration, Fe-S cluster biogenesis and protein lipoylation.

Drug targets for resistant malaria: Historic to future perspectives

New antimalarial targets are the prime need for the discovery of potent drug candidates. In order to fulfill this objective, antimalarial drug researches are focusing on promising targets in order to develop new drug candidates. Basic metabolism and biochemical process in the malaria parasite, i.e. Plasmodium falciparum can play an indispensable role in the identification of these targets. But, the emergence of resistance to antimalarial drugs is an escalating comprehensive problem with the progress of antimalarial drug development. The development of resistance has highlighted the need for the search of novel antimalarial molecules. The pharmaceutical industries are committed to new drug development due to the global recognition of this life threatening resistance to the currently available antimalarial therapy. The recent developments in the understanding of parasite biology are exhilarating this resistance issue which is further being ignited by malaria genome project. With this background of information, this review was aimed to highlights and provides useful information on various present and promising treatment approaches for resistant malaria, new progresses, pursued by some innovative targets that have been explored till date. This review also discusses modern and futuristic multiple approaches to antimalarial drug discovery and development with pictorial presentations highlighting the various targets, that could be exploited for generating promising new drugs in the future for drug resistant malaria.

Production of Medium Chain Fatty Acids by Yarrowia lipolytica: Combining Molecular Design and TALEN to Engineer the Fatty Acid Synthase

Yarrowia lipolytica is a promising organism for the production of lipids of biotechnological interest and particularly for biofuel. In this study, we engineered the key enzyme involved in lipid biosynthesis, the giant multifunctional fatty acid synthase (FAS), to shorten chain length of the synthesized fatty acids. Taking as starting point that the ketoacyl synthase (KS) domain of Yarrowia lipolytica FAS is directly involved in chain length specificity, we used molecular modeling to investigate molecular recognition of palmitic acid (C16 fatty acid) by the KS. This enabled to point out the key role of an isoleucine residue, I1220, from the fatty acid binding site, which could be targeted by mutagenesis. To address this challenge, TALEN (transcription activator-like effector nucleases)-based genome editing technology was applied for the first time to Yarrowia lipolytica and proved to be very efficient for inducing targeted genome modifications. Among the generated FAS mutants, those having a bulky aromatic amino acid residue in place of the native isoleucine at position 1220 led to a significant increase of myristic acid (C14) production compared to parental wild-type KS. Particularly, the best performing mutant, I1220W, accumulates C14 at a level of 11.6% total fatty acids. Overall, this work illustrates how a combination of molecular modeling and genome-editing technology can offer novel opportunities to rationally engineer complex systems for synthetic biology.

Engineering fungal de novo fatty acid synthesis for short chain fatty acid production

Fatty acids (FAs) are considered strategically important platform compounds that can be accessed by sustainable microbial approaches. Here we report the reprogramming of chain-length control of Saccharomyces cerevisiae fatty acid synthase (FAS). Aiming for short-chain FAs (SCFAs) producing baker's yeast, we perform a highly rational and minimally invasive protein engineering approach that leaves the molecular mechanisms of FASs unchanged. Finally, we identify five mutations that can turn baker's yeast into a SCFA producing system. Without any further pathway engineering, we achieve yields in extracellular concentrations of SCFAs, mainly hexanoic acid (C₆-FA) and octanoic acid (C₈-FA), of 464 mg l⁻¹ in total. Furthermore, we succeed in the specific production of C₆- or C₈-FA in extracellular concentrations of 72 and 245 mg l⁻¹, respectively. The presented technology is applicable far beyond baker's yeast, and can be plugged into essentially all currently available FA overproducing microorganisms.

The production of short chain fatty acids by microorganisms has numerous industrial and biofuel applications. Here the authors reprogramme S. cerevisiae fatty acid synthase with five mutations to produce C6- and C8-fatty acids and identify thioesterases responsible for hydrolysis of short chain acyl-CoA hydrolysis.

Engineering fatty acid synthases for directed polyketide production

In this study, we engineered fatty acid synthases (FAS) for the biosynthesis of short-chain fatty acids and polyketides, guided by a combined in vitro and in silico approach. Along with exploring the synthetic capability of FAS, we aim to build a foundation for efficient protein engineering, with the specific goal of harnessing evolutionarily related megadalton-scale polyketide synthases (PKS) for the tailored production of bioactive natural compounds.

Design, synthesis, and biological evaluation of chrysin derivatives as potential FabH inhibitors

New series of chrysin derivatives (4a-4t) were designed and synthesized by introducing different substituted piperazines at C-7 position. Their inhibitory effects on FabH were evaluated using two Gram-negative bacterial strains, Escherichia coli and Pseudomonas aeruginosa, and two Gram-positive bacterial strains, Bacillus subtilis and Staphylococcus aureus. To our delight, most of these compounds exhibited a dramatic increase in inhibitory potency, compared with the control positive drugs. Among them, compound 4s exhibited the most potent inhibitory activity with IC₅₀ values of 5.78 ± 0.24 μm inhibiting E. coli FabH and potent antibacterial activity against S. aureus and E. coli with MIC of 1.25 ± 0.01, 1.15 ± 0.12 μg/mL, respectively, comparing to the control positive drugs penicillin G (7.56 ± 0.30 μm). Docking simulation was performed to position compound 4s into the FabH active site, and the result showed that compound 4s could bind well with the FabH as potent FabH inhibitor.

Mitochondrial fatty acid synthesis, fatty acids and mitochondrial physiology

Mitochondria and fatty acids are tightly connected to a multiplicity of cellular processes that go far beyond mitochondrial fatty acid metabolism. In line with this view, there is hardly any common metabolic disorder that is not associated with disturbed mitochondrial lipid handling. Among other aspects of mitochondrial lipid metabolism, apparently all eukaryotes are capable of carrying out de novo fatty acid synthesis (FAS) in this cellular compartment in an acyl carrier protein (ACP)-dependent manner. The dual localization of FAS in eukaryotic cells raises the questions why eukaryotes have maintained the FAS in mitochondria in addition to the "classic" cytoplasmic FAS and what the products are that cannot be substituted by delivery of fatty acids of extramitochondrial origin. The current evidence indicates that mitochondrial FAS is essential for cellular respiration and mitochondrial biogenesis. Although both β-oxidation and FAS utilize thioester chemistry, CoA acts as acyl-group carrier in the breakdown pathway whereas ACP assumes this role in the synthetic direction. This arrangement metabolically separates these two pathways running towards opposite directions and prevents futile cycling. A role of this pathway in mitochondrial metabolic sensing has recently been proposed. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.

Design, synthesis and biological evaluation of metronidazole-thiazole derivatives as antibacterial inhibitors

A series of metronidazole-thiazole derivatives has been designed, synthesized and evaluated as potential antibacterial inhibitors. All the synthesized compounds were determined by elemental analysis, 1H NMR and MS. They were also tested for antibacterial activity against Escherichia coli, Bacillus thuringiensis, Bacillus subtilis and Pseudomonas aeruginosa as well as for the inhibition to FabH. The results showed that compound 5e exhibited the most potent inhibitory activity against E. coli FabH with IC50 of 4.9μM. Molecular modeling simulation studies were performed in order to predict the biological activity of proposed compounds. Toxicity assay of compounds 5a, 5b, 5d, 5e, 5g and 5i showed that they were noncytotoxic against human macrophage. The results revealed that these compounds offered remarkable viability.

Analyses of cobalt-ligand and potassium-ligand bond lengths in metalloproteins: trends and patterns

Cobalt and potassium are biologically important metal elements that are present in a large array of proteins. Cobalt is mostly found in vivo associated with a corrin ring, which represents the core of the vitamin B12 molecule. Potassium is the most abundant metal in the cytosol, and it plays a crucial role in maintaining membrane potential as well as correct protein function. Here, we report a thorough analysis of the geometric properties of cobalt and potassium coordination spheres that was performed with high resolution on a representative set of structures from the Protein Data Bank and complemented by quantum mechanical calculations realized at the DFT level of theory (B3LYP/ SDD) on mononuclear model systems. The results allowed us to draw interesting conclusions on the structural characteristics of both Co and K centers, and to evaluate the importance of effects such as their association energies and intrinsic thermodynamic stabilities. Overall, the results obtained provide useful data for enhancing the atomic models normally applied in theoretical and computational studies of Co or K proteins performed at the quantum mechanical level, and for developing molecular mechanical parameters for treating Co or K coordination spheres in molecular mechanics or molecular dynamics studies.

4-methylene-2-octyl-5-oxotetrahydrofuran-3-carboxylic acid (C75), an inhibitor of fatty-acid synthase, suppresses the mitochondrial fatty acid synthesis pathway and impairs mitochondrial function

4-Methylene-2-octyl-5-oxotetrahydrofuran-3-carboxylic acid (C75) is a synthetic fatty-acid synthase (FASN) inhibitor with potential therapeutic effects in several cancer models. Human mitochondrial β-ketoacyl-acyl carrier protein synthase (HsmtKAS) is a key enzyme in the newly discovered mitochondrial fatty acid synthesis pathway that can produce the substrate for lipoic acid (LA) synthesis. HsmtKAS shares conserved catalytic domains with FASN, which are responsible for binding to C75. In our study, we explored the possible effect of C75 on HsmtKAS and mitochondrial function. C75 treatment decreased LA content, impaired mitochondrial function, increased reactive oxygen species content, and reduced cell viability. HsmtKAS but not FASN knockdown had an effect that was similar to C75 treatment. In addition, an LA supplement efficiently inhibited C75-induced mitochondrial dysfunction and oxidative stress. Overexpression of HsmtKAS showed cellular protection against low dose C75 addition, whereas there was no protective effect upon high dose C75 addition. In summary, the mitochondrial fatty acid synthesis pathway has a vital role in mitochondrial function. Besides FASN, C75 might also inhibit HsmtKAS, thereby reducing LA production, impairing mitochondrial function, and potentially having toxic effects. LA supplements sufficiently ameliorated the toxicity of C75, showing that a combination of C75 and LA may be a reliable cancer treatment.

Synthesis and antibacterial evaluation of novel Schiff's base derivatives of nitroimidazole nuclei as potent E. coli FabH inhibitors

Series of novel Schiff's base derivatives have been synthesized. Compound 10q showed the most potent inhibitory activity (IC₅₀ = 2.6883 μM).

Discovery of novel selective inhibitors of Staphylococcus aureus β-ketoacyl acyl carrier protein synthase III

β-Ketoacyl-acyl carrier protein synthase III (KAS III) is a condensing enzyme in bacterial fatty acid synthesis and a potential target while designing novel antibiotics. In our previous report, we discovered the lead compound YKAs3003, which serves as an inhibitor of Escherichia coli KAS III (ecKAS III), and determined a reliable pharmacophore map from in silico screening. In this study, we determined two pharmacophore maps from receptor-oriented pharmacophore-based in silico screening of the x-ray structure of Staphylococcus aureus KAS III (saKAS III) to identify potent saKAS III inhibitors. We discovered a new potential inhibitor (6) with broad-spectrum antimicrobial activity and 0.8 nM binding affinity for saKAS III, proving the reliability of our pharmacophore map. Using optimization procedures, we identified three new antimicrobial saKAS III inhibitors: 6c (2,4-dichloro-benzoic acid (2,3,4-trihydroxy-benzylidene)-hydrazide), 6e (4-[(3-chloro-pyrazin-2-yl)-hydrazonomethyl]-benzene-1,3-diol), and 6 (4-[(5-trifluoromethyl-pyridin-2-yl)-hydrazonomethyl]-benzene-1,3-diol). All three inhibitors have a novel 4-hydrazonomethyl-benzene-1,3-diol core structure. These inhibitors exhibited high binding affinity to saKAS III and highly selective antimicrobial activities against S. aureus and methicillin-resistant S. aureus, with minimal inhibitory concentration values of 1-2 μg/mL.

Current understanding of fatty acid biosynthesis and the acyl carrier protein

FA (fatty acid) synthesis represents a central, conserved process by which acyl chains are produced for utilization in a number of end-products such as biological membranes. Central to FA synthesis, the ACP (acyl carrier protein) represents the cofactor protein that covalently binds all fatty acyl intermediates via a phosphopantetheine linker during the synthesis process. FASs (FA synthases) can be divided into two classes, type I and II, which are primarily present in eukaryotes and bacteria/plants respectively. They are characterized by being composed of either large multifunctional polypeptides in the case of type I or consisting of discretely expressed mono-functional proteins in the type II system. Owing to this difference in architecture, the FAS system has been thought to be a good target for the discovery of novel antibacterial agents, as exemplified by the antituberculosis drug isoniazid. There have been considerable advances in this field in recent years, including the first high-resolution structural insights into the type I mega-synthases and their dynamic behaviour. Furthermore, the structural and dynamic properties of an increasing number of acyl-ACPs have been described, leading to an improved comprehension of this central carrier protein. In the present review we discuss the state of the understanding of FA synthesis with a focus on ACP. In particular, developments made over the past few years are highlighted.

Structural basis for different specificities of acyltransferases associated with the human cytosolic and mitochondrial fatty acid synthases

Animals employ two systems for the de novo biosynthesis of fatty acids: a megasynthase complex in the cytosol (type I) that produces mainly palmitate, and an ensemble of freestanding enzymes in the mitochondria (type II) that produces mainly octanoyl moieties. The acyltransferases responsible for initiation of fatty acid biosynthesis in the two compartments are distinguished by their different substrate specificities: the type I enzyme transfers both the acetyl primer and the malonyl chain extender, whereas the type II enzyme is responsible for translocation of only the malonyl substrate. Crystal structures for the type I and II enzymes, supported by in silico substrate docking studies and mutagenesis experiments that alter their respective specificities, reveal that, although the two enzymes adopt a similar overall fold, subtle differences at their catalytic centers account for their different specificities.

Novel E. coli beta-ketoacyl-acyl carrier protein synthase III inhibitors as targeted antibiotics

Beta-ketoacyl-acyl carrier protein synthase (KAS) III is a condensing enzyme that initiates fatty acid biosynthesis in most bacteria. We determined three pharmacophore maps from receptor-oriented pharmacophore-based in silico screening of the X-ray structure of Escherichia coli KAS III (ecKAS III) and choose 16 compounds as candidate ecKAS III inhibitors. Binding inhibitors were characterized using saturation-transfer difference NMR spectroscopy (STD-NMR), and binding constants were determined with fluorescence quenching experiments. Based on the results, we propose that the antimicrobial compound, 4-cyclohexyliminomethyl-benzene-1,3-diol (YKAs3003), is a potent inhibitor of pathogenic KAS III, displaying minimal inhibitory concentration (MIC) values in the range 128-256 microg/mL against various bacteria.

Recent advances in the chemistry and biology of naturally occurring antibiotics

Ever since the world-shaping discovery of penicillin, nature's molecular diversity has been extensively screened for new medications and lead compounds in drug discovery. The search for agents intended to combat infectious diseases has been of particular interest and has enjoyed a high degree of success. Indeed, the history of antibiotics is marked with impressive discoveries and drug-development stories, the overwhelming majority of which have their origin in natural products. Chemistry, and in particular chemical synthesis, has played a major role in bringing naturally occurring antibiotics and their derivatives to the clinic, and no doubt these disciplines will continue to be key enabling technologies. In this review article, we highlight a number of recent discoveries and advances in the chemistry, biology, and medicine of naturally occurring antibiotics, with particular emphasis on total synthesis, analogue design, and biological evaluation of molecules with novel mechanisms of action.

Inhibition of the fungal fatty acid synthase type I multienzyme complex

Fatty acids are among the major building blocks of living cells, making lipid biosynthesis a potent target for compounds with antibiotic or antineoplastic properties. We present the crystal structure of the 2.6-MDa Saccharomyces cerevisiae fatty acid synthase (FAS) multienzyme in complex with the antibiotic cerulenin, representing, to our knowledge, the first structure of an inhibited fatty acid megasynthase. Cerulenin attacks the FAS ketoacyl synthase (KS) domain, forming a covalent bond to the active site cysteine C1305. The inhibitor binding causes two significant conformational changes of the enzyme. First, phenylalanine F1646, shielding the active site, flips and allows access to the nucleophilic cysteine. Second, methionine M1251, placed in the center of the acyl-binding tunnel, rotates and unlocks the inner part of the fatty acid binding cavity. The importance of the rotational movement of the gatekeeping M1251 side chain is reflected by the cerulenin resistance and the changed product spectrum reported for S. cerevisiae strains mutated in the adjacent glycine G1250. Platensimycin and thiolactomycin are two other potent inhibitors of KSs. However, in contrast to cerulenin, they show selectivity toward the prokaryotic FAS system. Because the flipped F1646 characterizes the catalytic state accessible for platensimycin and thiolactomycin binding, we superimposed structures of inhibited bacterial enzymes onto the S. cerevisiae FAS model. Although almost all side chains involved in inhibitor binding are conserved in the FAS multienzyme, a different conformation of the loop K1413-K1423 of the KS domain might explain the observed low antifungal properties of platensimycin and thiolactomycin.