RESUMO
Targeted protein degradation (TPD) has been established as a viable alternative to attenuate the function of a specific protein of interest in both biological and clinical contexts. The unique TPD mode-of-action has allowed previously undruggable proteins to become feasible targets, expanding the landscape of "druggable" properties and "privileged" target proteins. As TPD continues to evolve, a range of innovative strategies, which do not depend on recruiting E3 ubiquitin ligases as in proteolysis-targeting chimeras (PROTACs), have emerged. Here, we present an overview of direct lysosome- and proteasome-engaging modalities and discuss their perspectives, advantages, and limitations. We outline the chemical composition, biochemical activity, and pharmaceutical characteristics of each degrader. These alternative TPD approaches not only complement the first generation of PROTACs for intracellular protein degradation but also offer unique strategies for targeting pathologic proteins located on the cell membrane and in the extracellular space.
Assuntos
Lisossomos , Complexo de Endopeptidases do Proteassoma , Proteólise , Membrana Celular , Ubiquitina-Proteína LigasesRESUMO
Algae are key contributors to global carbon fixation and form the basis of many food webs. In nature, their growth is often supported or suppressed by microorganisms. The bacterium Pseudomonas protegens Pf-5 arrests the growth of the green unicellular alga Chlamydomonas reinhardtii, deflagellates the alga by the cyclic lipopeptide orfamide A, and alters its morphology [P. Aiyar et al., Nat. Commun. 8, 1756 (2017)]. Using a combination of Raman microspectroscopy, genome mining, and mutational analysis, we discovered a polyyne toxin, protegencin, which is secreted by P. protegens, penetrates the algal cells, and causes destruction of the carotenoids of their primitive visual system, the eyespot. Together with secreted orfamide A, protegencin thus prevents the phototactic behavior of C. reinhardtii A mutant of P. protegens deficient in protegencin production does not affect growth or eyespot carotenoids of C. reinhardtii Protegencin acts in a direct and destructive way by lysing and killing the algal cells. The toxic effect of protegencin is also observed in an eyeless mutant and with the colony-forming Chlorophyte alga Gonium pectorale These data reveal a two-pronged molecular strategy involving a cyclic lipopeptide and a conjugated tetrayne used by bacteria to attack select Chlamydomonad algae. In conjunction with the bloom-forming activity of several chlorophytes and the presence of the protegencin gene cluster in over 50 different Pseudomonas genomes [A. J. Mullins et al., bioRxiv [Preprint] (2021). https://www.biorxiv.org/content/10.1101/2021.03.05.433886v1 (Accessed 17 April 2021)], these data are highly relevant to ecological interactions between Chlorophyte algae and Pseudomonadales bacteria.
Assuntos
Toxinas Bacterianas/metabolismo , Toxinas Bacterianas/toxicidade , Chlamydomonas reinhardtii/efeitos dos fármacos , Pseudomonas/metabolismo , Carotenoides , Técnicas de Cocultura , Genoma BacterianoRESUMO
Prostaglandin E2 (PGE2) is known to be effective in regenerating tissues, and bimatoprost, an analog of PGF2α, has been approved by the FDA as an eyelash growth promoter and has been proven effective in human hair follicles. Thus, to enhance PGE2 levels while improving hair loss, we found dihydroisoquinolinone piperidinylcarboxy pyrazolopyridine (DPP), an inhibitor of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), using DeepZema®, an AI-based drug development program. Here, we investigated whether DPP improved hair loss in human follicle dermal papilla cells (HFDPCs) damaged by dihydrotestosterone (DHT), which causes hair loss. We found that DPP enhanced wound healing and the expression level of alkaline phosphatase in DHT-damaged HFDPCs. We observed that DPP significantly down-regulated the generation of reactive oxygen species caused by DHT. DPP recovered the mitochondrial membrane potential in DHT-damaged HFDPCs. We demonstrated that DPP significantly increased the phosphorylation levels of the AKT/ERK and activated Wnt signaling pathways in DHT-damaged HFDPCs. We also revealed that DPP significantly enhanced the size of the three-dimensional spheroid in DHT-damaged HFDPCs and increased hair growth in ex vivo human hair follicle organ culture. These data suggest that DPP exhibits beneficial effects on DHT-damaged HFDPCs and can be utilized as a promising agent for improving hair loss.
Assuntos
Folículo Piloso , Hidroxiprostaglandina Desidrogenases , Humanos , Folículo Piloso/efeitos dos fármacos , Folículo Piloso/metabolismo , Hidroxiprostaglandina Desidrogenases/metabolismo , Hidroxiprostaglandina Desidrogenases/antagonistas & inibidores , Di-Hidrotestosterona/farmacologia , Di-Hidrotestosterona/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Derme/metabolismo , Derme/citologia , Derme/efeitos dos fármacos , Células Cultivadas , Via de Sinalização Wnt/efeitos dos fármacos , Alopecia/tratamento farmacológico , Alopecia/metabolismo , Cicatrização/efeitos dos fármacos , Cabelo/efeitos dos fármacos , Cabelo/crescimento & desenvolvimento , Potencial da Membrana Mitocondrial/efeitos dos fármacos , Inibidores Enzimáticos/farmacologiaRESUMO
Proteomics has played a central role in the identification of reliable disease biomarkers, which are the basis of precision medicine, a promising approach for tackling recalcitrant diseases such as cancer, that elude conventional treatments. Among proteomic methodologies, targeted proteomics employing stable isotope-labeled (SIL) internal standards is particularly suited for the clinical translation of biomarker information owing to its high throughput and accuracy in the quantitative analysis of patient-derived proteomes. Using SIL internal standards ensures the utmost level of confidence in detection and precision in targeted MS experiments. For successfully establishing assays based on targeted proteomics, it is crucial to secure broad coverage when selecting the SIL standard peptide panel. However, cysteinyl peptides have often been excluded because of cysteine's high chemical reactivity. To address this limitation, a new cysteine building block was developed by incorporating a sulfhydryl group configured with an S-carbamidomethyl group, which is commonly used in proteome sampling. This compound was found to be chemically stable and applicable to a variety of solid-phase peptide synthesis (SPPS) campaigns. Furthermore, a direct comparison of the synthesized SIL peptides and tryptic endogenous peptides demonstrated the potential utility of an SPPS flow based on the new cysteine building block for improving the success of targeted proteomic applications.
Assuntos
Cisteína , Proteômica , Humanos , Compostos de Sulfidrila , Bioensaio , Peptídeos , ProteomaRESUMO
Various bacterial species are capable of producing highly modified fatty acid derivatives with conjugated triple bonds, which play important ecological roles as antifungals and toxins in mutualistic and pathogenic interactions. Furthermore, the terminal polyyne moiety is of interest as pharmacophore and as tag in bioorthogonal chemistry and live imaging. To gain insight into the assembly of these highly reactive natural products, we investigated tetrayne (caryoynencin and protegencin) biosynthesis genes (cay and pgn) from Trinickia caryophylli and Pseudomonas protegens. Pathway dissection and reconstitution in the heterologous host Burkholderia graminis revealed the genes minimally required for polyyne formation. Mutational analyses and biochemical assays demonstrated that polyyne biosynthesis is thiotemplated, involving a fatty acyl-AMP ligase, a designated acyl carrier protein, and a thioesterase. Heterologous expression of point-mutated desaturase genes showed that three desaturases work synergistically to introduce four triple bonds. These findings point to an intricate desaturase complex and provide important information for future bioengineering experiments.
Assuntos
Bactérias , Ácidos Graxos , Ácidos Graxos/química , Bactérias/metabolismo , Ácidos Graxos Dessaturases/genética , Ácidos Graxos Dessaturases/química , Ácidos Graxos Dessaturases/metabolismo , Poli-InosRESUMO
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMO
Caryoynencin is a toxic and antifungal fatty acid derivative produced by a number of plant-pathogenic and insect-protective bacteria (Trinickia caryophylli and Burkholderia spp.). In addition to the reactive tetrayne unit, the presence of an allylic alcohol moiety is critical for antimicrobial activities. By a combination of mutational analyses, heterologous expression and in vitro reconstitution experiments we show that the cytochromeâ P450 monooxygenase CayG catalyzes the complex transformation of a saturated carbon backbone into an allylic alcohol. Unexpectedly, CayG employs a ferritin-like protein (CayK) or a rubredoxin (CayL) component for electron transport. A desaturation-hydroxylation sequence was deduced from a time-course study and in vitro biotransformations with pathway intermediates, substrate analogues, protegencin congeners from Pseudomonas protegens Pf-5, and synthetic derivatives. This unusual multifunctional oxygenase may inspire future biocatalytic applications.
Assuntos
Sistema Enzimático do Citocromo P-450 , Propanóis , Sistema Enzimático do Citocromo P-450/metabolismo , Hidroxilação , OxirreduçãoRESUMO
AprD4 is a radical S-adenosyl-l-methionine (SAM) enzyme catalyzing C3'-deoxygenation of paromamine to form 4'-oxo-lividamine. It is the only 1,2-diol dehydratase in the radical SAM enzyme superfamily that has been identified and characterized in vitro. The AprD4 catalyzed 1,2-diol dehydration is a key step in the biosynthesis of several C3'-deoxy-aminoglycosides. While the regiochemistry of the hydrogen atom abstraction catalyzed by AprD4 has been established, the mechanism of the subsequent chemical transformation remains not fully understood. To investigate the mechanism, several substrate analogues were synthesized and their fates upon incubation with AprD4 were analyzed. The results support a mechanism involving formation of a ketyl radical intermediate followed by direct elimination of the C3'-hydroxyl group rather than that of a gem-diol intermediate generated via 1,2-migration of the C3'-hydroxyl group to C4'. The stereochemistry of hydrogen atom incorporation after radical-mediated dehydration was also established.
Assuntos
Aminoglicosídeos/química , Enzimas/química , S-Adenosilmetionina/química , Catálise , Água/químicaRESUMO
Soft rot disease of edible mushrooms leads to rapid degeneration of fungal tissue and thus severely affects farming productivity worldwide. The bacterial mushroom pathogen Burkholderia gladioli pv. agaricicola has been identified as the cause. Yet, little is known about the molecular basis of the infection, the spatial distribution and the biological role of antifungal agents and toxins involved in this infectious disease. We combine genome mining, metabolic profiling, MALDI-Imaging and UV Raman spectroscopy, to detect, identify and visualize a complex of chemical mediators and toxins produced by the pathogen during the infection process, including toxoflavin, caryoynencin, and sinapigladioside. Furthermore, targeted gene knockouts and inâ vitro assays link antifungal agents to prevalent symptoms of soft rot, mushroom browning, and impaired mycelium growth. Comparisons of related pathogenic, mutualistic and environmental Burkholderia spp. indicate that the arsenal of antifungal agents may have paved the way for ancestral bacteria to colonize niches where frequent, antagonistic interactions with fungi occur. Our findings not only demonstrate the power of label-free, inâ vivo detection of polyyne virulence factors by Raman imaging, but may also inspire new approaches to disease control.
Assuntos
Agaricales/efeitos dos fármacos , Toxinas Bacterianas/análise , Imagem Molecular , Doenças das Plantas/induzido quimicamente , Agaricales/metabolismo , Antifúngicos/farmacologia , Toxinas Bacterianas/antagonistas & inibidores , Toxinas Bacterianas/metabolismo , Burkholderia gladioli/efeitos dos fármacos , Burkholderia gladioli/metabolismo , Burkholderia gladioli/patogenicidade , Testes de Sensibilidade MicrobianaRESUMO
Gentamicin B (GB), a valuable starting material for the preparation of the semisynthetic aminoglycoside antibiotic isepamicin, is produced in trace amounts by the wild-type Micromonospora echinospora. Though the biosynthetic pathway to GB has remained obscure for decades, we have now identified three hidden pathways to GB production via seven hitherto unknown intermediates in M. echinospora. The narrow substrate specificity of a key glycosyltransferase and the C6'-amination enzymes, in combination with the weak and unsynchronized gene expression of the 2'-deamination enzymes, limits GB production in M. echinospora. The crystal structure of the aminotransferase involved in C6'-amination explains its substrate specificity. Some of the new intermediates displayed similar premature termination codon readthrough activity but with reduced toxicity compared to the natural aminoglycoside G418. This work not only led to the discovery of unknown biosynthetic routes to GB, but also demonstrated the potential to mine new aminoglycosides from nature for drug discovery.
Assuntos
Gentamicinas/biossíntese , Gentamicinas/metabolismo , Aminoglicosídeos/biossíntese , Antibacterianos , Proteínas de Bactérias , Vias Biossintéticas , Expressão Gênica , Glicosiltransferases/biossíntese , Glicosiltransferases/metabolismo , Micromonospora/metabolismo , Especificidade por SubstratoRESUMO
In the version of this article originally published, reference to another structure of GenB1 was omitted (Dow, G. T., Thoden, J. B., & Holden, H. M. The three-dimensional structure of NeoB: an aminotransferase involved in the biosynthesis of neomycin. Protein Sci. 27, 945-956 (2018)). This paper is now cited as reference 32, and "Another structure of GenB1 was also reported independently during the revision of this article32" was added to the text in the Discussion section. This error has been corrected in the PDF and HTML versions of the article.
RESUMO
Covering: 1994 to 2019Owing to the rapid increase in nosocomial infections by antibiotic-resistant Acinetobacter baumannii and the paucity of effective treatment options for such infections, interest in the virulence factors involved in its successful dissemination and propagation in the human host have escalated in recent years. Acinetobacin, a siderophore of A. baumannii, is responsible for iron acquisition under nutritional depravation and has been shown to be one of the key virulence factors for this bacterium. In this Highlight, recent findings regarding various chemical and biological aspects of acinetobactin metabolism closely related to the fitness of A. baumannii at the infection sites have been described. In addition, several notable efforts for identifying novel anti-infectious agents based thereon have been discussed.
Assuntos
Acinetobacter baumannii/metabolismo , Antibacterianos/farmacologia , Proteínas de Bactérias/química , Imidazóis/metabolismo , Oxazóis/metabolismo , Acinetobacter baumannii/efeitos dos fármacos , Antibacterianos/química , Proteínas de Bactérias/metabolismo , Farmacorresistência Bacteriana , Humanos , Imidazóis/química , Ferro/metabolismo , Oxazóis/química , Sideróforos/metabolismo , Relação Estrutura-AtividadeRESUMO
Development of highly effective, safe, and fast-acting anti-depressants is urgently required for the treatment of major depressive disorder. It has been suggested that targeting 5-HT2A and 5-HT2C in addition to inhibition of serotonin reuptake may be beneficial in generating anti-depressant agents with better pharmacology and less adverse effects. We have developed phthalazinone-based compounds that potently bind to 5-HT2A, 5-HT2C, and the serotonin transporter. The representative compounds 11j and 11l displayed strong binding affinities against these targets, and showed favorable toxicity profiles as determined by hERG binding and CYP inhibition assays. Furthermore, these compounds presented promising anti-depressant effects comparable to fluoxetine and also synergistic effects with fluoxetine in forced swimming test, which implicates these compounds can be developed to help the treatment of major depressive disorder.
Assuntos
Antidepressivos/química , Azóis/química , Receptor 5-HT2A de Serotonina/química , Receptor 5-HT2C de Serotonina/química , Proteínas da Membrana Plasmática de Transporte de Serotonina/química , Animais , Antidepressivos/metabolismo , Antidepressivos/farmacologia , Comportamento Animal/efeitos dos fármacos , Desenho de Fármacos , Fluoxetina/química , Fluoxetina/farmacologia , Humanos , Concentração Inibidora 50 , Camundongos , Receptor 5-HT2A de Serotonina/metabolismo , Receptor 5-HT2C de Serotonina/metabolismo , Antagonistas do Receptor 5-HT2 de Serotonina/química , Antagonistas do Receptor 5-HT2 de Serotonina/metabolismo , Antagonistas do Receptor 5-HT2 de Serotonina/farmacologia , Proteínas da Membrana Plasmática de Transporte de Serotonina/metabolismo , Inibidores Seletivos de Recaptação de Serotonina/química , Inibidores Seletivos de Recaptação de Serotonina/metabolismo , Inibidores Seletivos de Recaptação de Serotonina/farmacologia , Relação Estrutura-AtividadeRESUMO
This report describes the synthesis of a library of fluorogenic carbapenemase substrates consisting of carbapenem derivatives, fluorescence dyes, and active cleavable linkers and their evaluation for specifically detecting carbapenemase-producing organisms (CPOs). We synthesized a series of compounds having three different types of linkers such as benzyl ether, carbamate, and amine using hydroxymethyl carbapenem 7a and hydroxyallyl carbapenem 7b as key intermediates. Probe 1b exhibited high stability and a prompt turn-on fluorescence signal upon hydrolysis by carbapenemases. In particular, the screening of clinical samples indicated that the probe 1b exhibited excellent selectivity to the CPOs over other ß-lactamases or non-carbapenemase producing bacteria, which may be of clinical use for the rapid and accurate detection of CPOs for timely diagnosis and treatment.
Assuntos
Bactérias/patogenicidade , Proteínas de Bactérias/química , Carbapenêmicos/química , Corantes Fluorescentes/uso terapêutico , beta-Lactamases/química , Humanos , Modelos MolecularesRESUMO
Here, we describe the synthesis of disubstituted pyrimidine derivatives and their biological evaluation as selective 5-HT2C agonists. To improve selectivity for 5-HT2C over other subtypes, we synthesized two series of disubstituted pyrimidines with fluorophenylalkoxy groups at either the 5-position or 4-position and varying cyclic amines at the 2-position. The in vitro cell-based assay and binding assay identified compounds 10a and 10f as potent 5-HT2C agonists. Further studies on selectivity to 5-HT subtypes and drug-like properties indicated that 2,4-disubstituted pyrimidine 10a showed a highly agonistic effect on the 5-HT2C receptor, with excellent selectivity, as well as exceptional drug-like properties, including high plasma and microsomal stability, along with low CYP inhibition. Thus, pyrimidine 10a could be considered a viable lead compound as a 5-HT2C selective agonist.
Assuntos
Pirimidinas/síntese química , Pirimidinas/farmacologia , Receptor 5-HT2C de Serotonina/química , Agonistas do Receptor 5-HT2 de Serotonina/síntese química , Agonistas do Receptor 5-HT2 de Serotonina/farmacologia , Técnicas de Química Sintética , Relação Dose-Resposta a Droga , Estabilidade de Medicamentos , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Estrutura Molecular , Ligação Proteica , Pirimidinas/química , Receptor 5-HT2C de Serotonina/metabolismo , Agonistas do Receptor 5-HT2 de Serotonina/química , Relação Estrutura-AtividadeRESUMO
Ketosynthase (KS) domains of modular typeâ I polyketide synthases (PKSs) typically catalyze the Claisen condensation of acyl and malonyl units to form linear chains. In stark contrast, the KS of the rhizoxin PKS branching module mediates a Michael addition, which sets the basis for a pharmacophoric δ-lactone moiety. The precise role of the KS was evaluated by site-directed mutagenesis, chemical probes, and biotransformations. Biochemical and kinetic analyses helped to dissect branching and lactonization reactions and unequivocally assign the entire sequence to the KS. Probing the range of accepted substrates with diverse synthetic surrogates in vitro, we found that the KS tolerates defined acyl chain lengths to produce five- to seven-membered lactones. These results show that the KS is multifunctional, as it catalyzes ß-branching and lactonization. Information on the increased product portfolio of the unusual, TE-independent on-line cyclization is relevant for synthetic biology approaches.
Assuntos
Bacillus amyloliquefaciens/enzimologia , Burkholderia/enzimologia , Lactonas/metabolismo , Policetídeo Sintases/metabolismo , Bacillus amyloliquefaciens/genética , Bacillus amyloliquefaciens/metabolismo , Burkholderia/genética , Burkholderia/metabolismo , Ciclização , Lactonas/química , Macrolídeos/química , Macrolídeos/metabolismo , Modelos Moleculares , Mutagênese Sítio-Dirigida , Policetídeo Sintases/química , Policetídeo Sintases/genética , Domínios Proteicos , Especificidade por SubstratoRESUMO
Mitsugumin 53 (MG53) is an E3 ligase that interacts with and ubiquitinates insulin receptor substrate-1 (IRS-1) in skeletal muscle; thus, an MG53-IRS-1 interaction disruptor (MID), which potentially sensitizes insulin signaling with an elevated level of IRS-1 in skeletal muscle, is an excellent candidate for treating insulin resistance. To screen for an MID, we developed a bimolecular luminescence complementation system using an N-terminal luciferase fragment fused with IRS-1 and a C-terminal luciferase fragment fused with an MG53 C14A mutant that binds to IRS-1 but does not have E3 ligase activity. An MID, which was discovered using the bimolecular luminescence complementation system, disrupted the molecular association of MG53 with IRS-1, thus abolishing MG53-mediated IRS-1 ubiquitination and degradation. Thus, the MID sensitized insulin signaling and increased insulin-elicited glucose uptake with an elevated level of IRS-1 in C2C12 myotubes. These data indicate that this MID holds promise as a drug candidate for treating insulin resistance.
Assuntos
Proteínas de Transporte/metabolismo , Proteínas Substratos do Receptor de Insulina/metabolismo , Insulina/metabolismo , Proteínas dos Microtúbulos/metabolismo , Músculo Esquelético/metabolismo , Proteínas Nucleares/metabolismo , Mapas de Interação de Proteínas/efeitos dos fármacos , Bibliotecas de Moléculas Pequenas/farmacologia , Fatores de Transcrição/metabolismo , Células Cultivadas , Humanos , Resistência à Insulina , Fibras Musculares Esqueléticas/citologia , Fibras Musculares Esqueléticas/efeitos dos fármacos , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/efeitos dos fármacos , Fosforilação/efeitos dos fármacos , Proteólise , Transdução de Sinais/efeitos dos fármacos , Proteínas com Motivo Tripartido , Ubiquitina-Proteína Ligases/metabolismo , UbiquitinaçãoRESUMO
Many cobalamin (Cbl)-dependent radical S-adenosyl-l-methionine (SAM) methyltransferases have been identified through sequence alignment and/or genetic analysis; however, few have been studied in vitro. GenK is one such enzyme that catalyzes methylation of the 6'-carbon of gentamicin X2 (GenX2) to produce G418 during the biosynthesis of gentamicins. Reported herein, several alternative substrates and fluorinated substrate analogs were prepared to investigate the mechanism of methyl transfer from Cbl to the substrate as well as the substrate specificity of GenK. Experiments with deuterated substrates are also shown here to demonstrate that the 6'-pro-R-hydrogen atom of GenX2 is stereoselectively abstracted by the 5'-dAdo· radical and that methylation occurs with retention of configuration at C6'. Based on these observations, a model of GenK catalysis is proposed wherein free rotation of the radical-bearing carbon is prevented and the radical SAM machinery sits adjacent rather than opposite to the Me-Cbl cofactor with respect to the substrate in the enzyme active site.
Assuntos
Vias Biossintéticas , Gentamicinas/metabolismo , Metiltransferases/metabolismo , S-Adenosilmetionina/metabolismo , Vitamina B 12/metabolismo , Domínio Catalítico , Metilação , Metiltransferases/química , Especificidade por SubstratoRESUMO
Total synthesis of the proposed structure of baulamycin A was performed. The spectral properties of the synthetic compound differ from those reported for the natural product. On the basis of comprehensive NMR study, we proposed two other possible structures for natural baulamycin A. Total syntheses of these two substances were performed, which enabled assignment of the correct structure of baulamycin A. Key features of the convergent and fully stereocontrolled route include Evans Aldol and Brown allylation reactions to construct the left fragment, a prolinol amide-derived alkylation/desymmetrization to install the methyl-substituted centers in the right fragment, and finally, a Carreira alkynylation to join both fragments. In addition, we have determined the inhibitory activities of novel baulamycin A derivatives against the enzyme SbnE. This SAR study provides useful insight into the design of novel SbnE inhibitors that overcome the drug resistance of pathogens, which cause life-threatening infections.
Assuntos
Inibidores Enzimáticos/síntese química , Álcoois Graxos/síntese química , Resorcinóis/síntese química , Alquilação , Farmacorresistência Bacteriana/efeitos dos fármacos , Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacologia , Álcoois Graxos/química , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Resorcinóis/química , Relação Estrutura-AtividadeRESUMO
The Diels-Alder reaction is a [4+2] cycloaddition reaction in which a cyclohexene ring is formed between a 1,3-diene and an electron-deficient alkene via a single pericyclic transition state. This reaction has been proposed as a key transformation in the biosynthesis of many cyclohexene-containing secondary metabolites. However, only four purified enzymes have thus far been implicated in biotransformations that are consistent with a Diels-Alder reaction, namely solanapyrone synthase, LovB, macrophomate synthase, and riboflavin synthase. Although the stereochemical outcomes of these reactions indicate that the product formation could be enzyme-guided in each case, these enzymes typically demonstrate more than one catalytic activity, leaving their specific influence on the cycloaddition step uncertain. In our studies of the biosynthesis of spinosyn A, a tetracyclic polyketide-derived insecticide from Saccharopolyspora spinosa, we identified a cyclase, SpnF, that catalyses a transannular [4+2] cycloaddition to form the cyclohexene ring in spinosyn A. Kinetic analysis demonstrates that SpnF specifically accelerates the ring formation reaction with an estimated 500-fold rate enhancement. A second enzyme, SpnL, was also identified as responsible for the final cross-bridging step that completes the tetracyclic core of spinosyn A in a manner consistent with a Rauhut-Currier reaction. This work is significant because SpnF represents the first example characterized in vitro of a stand-alone enzyme solely committed to the catalysis of a [4+2] cycloaddition reaction. In addition, the mode of formation of the complex perhydro-as-indacene moiety in spinosyn A is now fully established.