Mutasynthesis generates nine new pyrroindomycins.

Pyrroindomycins (PYRs) represent the only spirotetramate natural products discovered in nature, and possess potent activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Their unique structure and impressive biological activities make them attractive targets for synthesis and biosynthesis; however, the discovery and generation of new PYRs remains challenging. To date, only the initial components A and B have been reported. Herein, we report a mutasynthesis approach for the generation of nine new PYRs with varying acyl modifications on their deoxy-trisaccharide moieties. This was achieved by blocking the formation of the acyl group 1,8-dihydropyrrolo[2,3-b]indole (DHPI) via gene pyrK1 inactivation and supplying chemical acyl precursors. The gene pyrK1 encodes a DUF1864 family protein that probably catalyzes the oxidative transformation of L-tryptophan to DHPI, and its deletion results in the abolishment of DHPI-containing PYRs and the accumulation of three new PYRs either without acyl modification or with DHPI replaced by benzoic acid and pyrrole-2-carboxylic acid. Capitalizing on the capacity of the ΔpyrK1 mutant to produce new PYRs, we have successfully developed a mutasynthesis strategy for the generation of six novel PYR analogs with various aromatic acid modifications on their deoxy-trisaccharide moieties, showcasing the potential for generating structurally diverse PYRs. Overall, this research contributes significantly to understanding the biosynthesis of PYRs and offers valuable perspectives on their structural diversity.

Biocatalytic Steroidal 9α-Hydroxylation and Fragmentation Enable the Concise Chemoenzymatic Synthesis of 9,10-Secosteroids.

9,10-Secosteroids are an important group of marine steroids with diverse biological activities. Herein, we report a chemoenzymatic strategy for the concise, modular, and scalable synthesis of ten naturally occurring 9,10-secosteroids from readily available steroids in three to eight steps. The key feature lies in utilizing a Rieske oxygenase-like 3-ketosteroid 9α-hydroxylase (KSH) as the biocatalyst to achieve efficient C9-C10 bond cleavage and A-ring aromatization of tetracyclic steroids through 9α-hydroxylation and fragmentation. With synthesized 9,10-secosteroides, structure-activity relationship was evaluated based on bioassays in terms of previously unexplored anti-infective activity. This study provides experimental evidence to support the hypothesis that the biosynthetic pathway through which 9,10-secosteroids are formed in nature shares a similar 9α-hydroxylation and fragmentation cascade. In addition to the development of a biomimetic approach for 9,10-secosteroid synthesis, this study highlights the great potential of chemoenzymatic strategies in chemical synthesis.

The antipsychotic drug penfluridol inhibits N-linked glycoprotein processing and enhances T-cell-mediated tumor immunity.

Aberrant N-linked glycosylation is a prominent feature of cancers. Perturbance of oligosaccharide structure on cell surfaces directly affects key processes in tumor development and progression. In spite of the critical role played by N-linked glycans in tumor biology, the discovery of small molecules that specifically disturbs the N-linked glycans is still under investigation. To identify more saccharide-structure-perturbing compounds, a repurposed drug screen by using a library consisting of 1530 FDA-approved drugs was performed. Interestingly, an antipsychotic drug, penfluridol, was identified as being able to decrease cell surface Wheat germ agglutinin (WGA) staining. In the presence of penfluridol, cell membrane glycoproteins PD-L1 shifted to a lower molecular weight. Further studies demonstrated that penfluridol treatment caused an accumulation of high-mannose oligosaccharides, especially Man5-7GlcNAc2 glycan structures. Mechanistically, this effect is due to direct targeting of MAN1A1 mannosidase, a Golgi enzyme involved in N-glycan maturation. Moreover, we found that altered glycosylation of PD-L1 caused by penfluridol disrupted interactions between PD-1 and PD-L1, resulting in activation of T-cell tumor immunity. In a mouse xenograft and glioma model, penfluridol enhanced the anti-tumor effect of the anti-PD-L1 antibody in vivo. Overall, these findings revealed an important biological activity of the antipsychotic drug penfluridol as an inhibitor of glycan processing and proposed a repurposed use of penfluridol in anti-tumor therapy through activation of T-cell immunity.

Biocatalytic Fluoroalkylation Using Fluorinated S-Adenosyl-l-methionine Cofactors.

Modification of organic molecules with fluorine functionalities offers a critical approach to develop new pharmaceuticals. Here, we report a multienzyme strategy for biocatalytic fluoroalkylation using S-adenosyl-l-methionine (SAM)-dependent methyltransferases (MTs) and fluorinated SAM cofactors prepared from ATP and fluorinated l-methionine analogues by an engineered human methionine adenosyltransferase hMAT2AI322A. This work introduces the first example of biocatalytic 3,3-difluoroallylation. Importantly, this strategy can be applied to late-stage site-selective fluoroalkylation of complex molecule vancomycin with conversions up to 99%.

Formation and Loading of a (2S)-2-Ethylmalonamyl Starter Unit in the Assembly Line of Polyketide-Nonribosomal Peptide Hybrid Sanglifehrin A.

Sanglifehrin A (SFA) is a spirolactam-conjugated, 22-membered macrolide with remarkable immunosuppressive and antiviral activities. This macrolide is a result of a hybrid polyketide synthase (PKS)-nonribosomal peptide synthetase (NRPS) assembly line that utilizes (2S)-2-ethylmalonamyl as a starter unit. Here, we report that the formation and loading of this starter unit in the SFA assembly line involve two unusual enzymatic reactions that occur on a discrete acyl carrier protein (ACP), SfaO. An amide synthetase, SfaP, catalyzes the amidation of (2S)-2-ethylmalonyl in a SfaO-dependent manner. Then, a ß-ketoacyl-ACP synthase III-like protein, SfaN, transfers resultant (2S)-2-ethylmalonamyl from SfaO onto the loading ACP domain of the hybrid PKS-NRPS assembly line to prime SFA biosynthesis. Both SfaP and SfaN display promiscuous activities. This study furthers the appreciation of assembly line chemistry, as a new paradigm for unusual building block formation and incorporation is provided.

Enzymatic α-Ketothioester Decarbonylation Occurs in the Assembly Line of Barbamide for Skeleton Editing.

The decarbonylation reaction has been developed significantly in organic chemistry as an effective approach to various synthetic applications, but enzymatic precedents for this reaction are rare. Based on investigations into the hybrid nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) assembly line of barbamide, we report an on-line α-ketothioester decarbonylation reaction that leads to one-carbon truncation of the elongating skeleton. This enzymatic editing reaction occurs in the first round of lipopeptide extension and modification involving the multienzymes BarE and BarF, which successively house an NRPS module to initiate the biosynthesis and a PKS module to catalyze the first round of chain extension. Starting with processing a leucine-derived α-ketoacyl starter, the ketosynthase domain in BarE displays an unusual dual activity that results in net one-carbon chain elongation. It extrudes carbon monoxide from α-keto-isocaproyl thioester and then mediates decarboxylative condenses of the resultant isovaleryl thioester with malonyl thioester to form a diketide intermediate, followed by BarF-based O-methylation to stabilize the enol form of the ß-carbonyl and afford an unusual E-double bond. Biochemical characterization, chemical synthesis, computational analysis, and the experimental outcome of site-directed mutagenesis illustrate the extraordinary catalytic capability of this ketosynthase domain. This work furthers the appreciation of assembly line chemistry and opens the door to new approaches for skeleton editing/engineering of related molecules using synthetic biology approaches.

A cyclase that catalyses competing 2 + 2 and 4 + 2 cycloadditions.

Cycloaddition reactions are among the most widely used reactions in chemical synthesis. Nature achieves these cyclization reactions with a variety of enzymes, including Diels-Alderases that catalyse concerted 4 + 2 cycloadditions, but biosynthetic enzymes with 2 + 2 cyclase activity have yet to be discovered. Here we report that PloI4, a ß-barrel-fold protein homologous to the exo-selective 4 + 2 cyclase that functions in the biosynthesis of pyrroindomycins, catalyses competitive 2 + 2 and 4 + 2 cycloaddition reactions. PloI4 is believed to catalyse an endo-4 + 2 cycloaddition in the biosynthesis of pyrrolosporin A; however, when the substrate precursor of pyrroindomycins was treated with PloI4, an exo-2 + 2 adduct was produced in addition to the exo- and endo-4 + 2 adducts. Biochemical characterizations, computational analyses, (co)crystal structures and mutagenesis outcomes have allowed the catalytic versatility of PloI4 to be rationalized. Mechanistic studies involved the directed engineering of PloI4 to variants that produced the exo-4 + 2, endo-4 + 2 or exo-2 + 2 product preferentially. This work illustrates an enzymatic thermal 2 + 2 cycloaddition and provides evidence of a process through which an enzyme evolves along with its substrate for specialization and activity improvement.

Structure-Based Mechanistic Insights into ColB1, a Flavoprotein Functioning in-trans in the 2,2'-Bipyridine Assembly Line for Cysteine Dehydrogenation.

The recruitment of trans-acting enzymes by nonribosomal peptide synthetase (NRPS) assembly line is rarely reported. ColB1 is a flavin-dependent dehydrogenase that is recruited by an NRPS terminal condensation domain (Ct domain) and catalyzes peptidyl carrier protein (PCP)-tethered cysteine dehydrogenation in collismycin biosynthesis. We here report the crystal structure of ColB1 complexed with FAD and reveal a typical structural fold of acyl-CoA dehydrogenases (ACADs). However, ColB1 shows distinct structural features from ACADs in substrate recognition both at the entrance of and inside the active site. Site-directed mutagenesis and substrate modeling establish a Glu393-mediated catalytic mechanism, by which the cysteine substrate is sandwiched between Glu393 and FAD to facilitate Cα proton abstraction and Cß hydride migration. A ColB1-PCP-Ct complex model is generated, providing structural basis for the unique recruitment interactions between ColB1 and the associated NRPS. These results add insights into the mechanisms by which trans-acting enzymes function in an assembly line.

An updated HACOR score for predicting the failure of noninvasive ventilation: a multicenter prospective observational study.

BACKGROUND: Heart rate, acidosis, consciousness, oxygenation, and respiratory rate (HACOR) have been used to predict noninvasive ventilation (NIV) failure. However, the HACOR score fails to consider baseline data. Here, we aimed to update the HACOR score to take into account baseline data and test its predictive power for NIV failure primarily after 1-2 h of NIV. METHODS: A multicenter prospective observational study was performed in 18 hospitals in China and Turkey. Patients who received NIV because of hypoxemic respiratory failure were enrolled. In Chongqing, China, 1451 patients were enrolled in the training cohort. Outside of Chongqing, another 728 patients were enrolled in the external validation cohort. RESULTS: Before NIV, the presence of pneumonia, cardiogenic pulmonary edema, pulmonary ARDS, immunosuppression, or septic shock and the SOFA score were strongly associated with NIV failure. These six variables as baseline data were added to the original HACOR score. The AUCs for predicting NIV failure were 0.85 (95% CI 0.84-0.87) and 0.78 (0.75-0.81) tested with the updated HACOR score assessed after 1-2 h of NIV in the training and validation cohorts, respectively. A higher AUC was observed when it was tested with the updated HACOR score compared to the original HACOR score in the training cohort (0.85 vs. 0.80, 0.86 vs. 0.81, and 0.85 vs. 0.82 after 1-2, 12, and 24 h of NIV, respectively; all p values < 0.01). Similar results were found in the validation cohort (0.78 vs. 0.71, 0.79 vs. 0.74, and 0.81 vs. 0.76, respectively; all p values < 0.01). When 7, 10.5, and 14 points of the updated HACOR score were used as cutoff values, the probability of NIV failure was 25%, 50%, and 75%, respectively. Among patients with updated HACOR scores of ≤ 7, 7.5-10.5, 11-14, and > 14 after 1-2 h of NIV, the rate of NIV failure was 12.4%, 38.2%, 67.1%, and 83.7%, respectively. CONCLUSIONS: The updated HACOR score has high predictive power for NIV failure in patients with hypoxemic respiratory failure. It can be used to help in decision-making when NIV is used.

Comparison of CRP, Procalcitonin, Neutrophil Counts, Eosinophil Counts, sTREM-1, and OPN between Pneumonic and Nonpneumonic Exacerbations in COPD Patients.

Introduction: The patients with community-acquired pneumonia (CAP) and acute exacerbations of COPD (AECOPD) could have a higher risk of acute and severe respiratory illness than those without CAP in AECOPD. Consequently, early identification of pneumonia in AECOPD is quite important. Methods. 52 subjects with AECOPD + CAP and 93 subjects with AECOPD from two clinical centers were enrolled in this prospective observational study. The values of osteopontin (OPN), soluble triggering receptor expressed on myeloid cells-1 (sTREM-1), C-reactive protein (CRP), procalcitonin (PCT), eosinophil (EOS) counts, and neutrophil (Neu) counts in blood on the first day of admission and clinical symptoms were compared in AECOPD and AECOPD + CAP. In addition, subgroup analyses of biomarker difference were conducted based on the current use of inhaled glucocorticoids (ICS) or systemic corticosteroids (SCS). Results: Patients with AECOPD + CAP had increased sputum volume, sputum purulence, diabetes mellitus, and longer hospital stays than AECOPD patients (p < 0.05). A clinical logistic regression model showed among the common clinical symptoms, purulent sputum can independently predict pneumonia in AECOPD patients after adjusting for a history of diabetes. At day 1, AECOPD + CAP patients had higher values of Neu, CRP, PCT, and OPN, while serum sTREM-1 levels and EOS counts were similar in the two groups. CRP fared best at predicting AECOPD with CAP (p < 0.05 for the test of difference), while OPN had similar accuracy with Neu, PCT, and purulent sputum (p > 0.05 for the test of difference). Multivariate analysis, including clinical symptoms and biomarkers, suggested that CRP ≥15.8 mg/dL at day 1 was a only promising predictor of pneumonia in AECOPD. CRP and OPN were not affected by ICS or SCS. Conclusions: CRP ≥15.8 mg/dL is an ideal promising predictor of pneumonia in AECOPD, and its plasma level is not affected by ICS or SCS. The diagnostic performance of CRP is not significantly improved when combined with clinical symptoms or other markers (OPN, PCT, and Neu).

Black soldier fly larvae effectively degrade lincomycin from pharmaceutical industry wastes.

Lincomycin fermentation residues (LFR) are the byproducts from the pharmaceutical industry, and contain high concentrations of antibiotics that could pose a threat to the environment. Here, we report that black soldier fly larvae (BSFL) and associated microbiota can effectively degrade LFR and accelerate the degradation of lincomycin in LFR. The degradation rate of lincomycin in LFR can reach 84.9% after 12 days of BSFL-mediated bioconversion, which is 3-fold greater than that accomplished with natural composting. The rapid degradation was partially carried out by the BSFL-associated microbiota, contributing 22.0% of the degradation in the final composts. Based on microbiome analysis, we found that the structure of microbiota from both BSFL guts and BSFL composts changed significantly during the bioconversion, and that several bacterial genera were correlated with lincomycin degradation. The roles of the associated microbiota in the degradation were further verified by the ability of two larval intestinal bacterial isolates and one bacterial isolate from BSFL composts to lincomycin degradation. The synergy between BSFL and the isolated strains resulted in a 2-fold increase in degradation compared to that achieved by microbial degradation alone. Furthermore, we determined that the degradation was correlated with the induction of several antibiotic resistant genes (ARGs) associated with lincomycin degradation in larval guts and BSFL composts. Moreover, the environmental conditions in the BSFL composts were found to be conducive to the degradation. In conclusion, these findings demonstrate that the BSFL-mediated bioconversion of LFR could effectively reduce residual lincomycin and that the associated microbiota play crucial roles in the process.

Investigation of 2,2'-Bipyridine Biosynthesis Reveals a Common Two-Component System for Aldehydes Production by Carboxylate Reduction.

Here, we report a two-component enzymatic system that efficiently catalyzes the reduction of a carboxylate to an aldehyde in the biosynthesis of 2,2'-bipyridine antibiotics caerulomycins. The associated paradigm involves the activation of carboxylate by ATP-dependent adenylation protein CaeF, followed by its reduction catalyzed by CaeB2, a new class of NADPH-dependent aldehyde dehydrogenase (ALDH) that directly reduces AMP-conjugated carboxylate, which is distinct from the known aldehyde-producing enzymes that reduce ACP- or CoA-conjugated carboxylates.

Knockdown of long noncoding RNA MIAT attenuates cigarette smoke-induced airway remodeling by downregulating miR-29c-3p-HIF3A axis.

Chronic obstructive pulmonary disease (COPD) is a global public health issue and is defined as persistent airflow limitation. COPD is a major cause of morbidity and mortality worldwide. Long noncoding RNAs are involved in the course of pulmonary diseases. Here, we revealed that a long noncoding RNA called myocardial-infarction-associated transcript (MIAT) is upregulated in lung tissues of cigarette smoke (CS)-exposed mice. Knockdown of MIAT attenuated CS or CS-extract-induced inflammatory processes, epithelial-mesenchymal transition (EMT), and collagen deposition. Moreover, according to bioinformatic analyses and luciferase reporter assays, MIAT binds to microRNA-29c-3p (miR-29c-3p) and upregulates hypoxia-inducible factor 3 alpha (HIF3A), a target gene of miR-29c-3p. When the MIAT-specific short hairpin RNA and an miR-29c-3p inhibitor were cotransfected into cells, the inhibitor reversed the effects of MIAT knockdown on cell proliferation, apoptosis, inflammation, EMT, and collagen deposition. Overall, these results indicate that MIAT participates in CS-induced EMT and airway remodeling in COPD by upregulating miR-29c-3p-HIF3A axis output, thereby offering a novel promising biomarker for the assessment of COPD exacerbation induced by CS exposure.

Association between ARDS Etiology and Risk of Noninvasive Ventilation Failure.

Rationale: The etiology of acute respiratory distress syndrome (ARDS) may play an important role in the failure of noninvasive ventilation (NIV). Objectives: To explore the association between ARDS etiology and risk of NIV failure. Methods: A multicenter prospective observational study was performed in 17 intensive care units in China from September 2017 to December 2019. Patients with ARDS who used NIV as a first-line therapy were enrolled. The etiology of ARDS was recorded at study entry. Results: A total of 306 patients were enrolled. Of the patients, 146 were classified as having pulmonary ARDS (ARDSp) and 160 were classified as having extrapulmonary ARDS (ARDSexp). From initiation to 24 hours of NIV, the respiratory rate, heart rate, arterial oxygen pressure (PaO2)/fraction of inspired oxygen (FiO2), and arterial carbon dioxide pressure improved slower in patients with ARDSp than those with ARDSexp. Patients with ARDSp experienced more NIV failure (55% vs. 28%; P < 0.01) and higher 28-day mortality (47% vs. 14%; P < 0.01). The adjusted odds ratios of NIV failure and 28-day mortality were 5.47 (95% confidence interval [CI], 3.04-9.86) and 10.13 (95% CI, 5.01-20.46), respectively. In addition, we combined the presence of ARDSp, presence of septic shock, age, nonpulmonary sequential organ failure assessment score, respiratory rate at 1-2 hours of NIV, and PaO2/FiO2 at 1-2 h of NIV to develop a risk score of NIV failure. With the increase of the risk score, the rate of NIV failure increased. The area under the curve of the receiver operating characteristic was 0.84 (95% CI, 0.79-0.89) and 0.81 (0.69-0.92) in the training and validation cohorts, respectively. Using 5.5 as cutoff value to predict NIV failure, the sensitivity and specificity was good. Conclusions: Among patients with ARDS who used NIV as a first-line therapy, ARDSp was associated with slower improvement, more NIV failure, and higher 28-day mortality than ARDSexp. The risk score combined presence of ARDSp, presence of septic shock, age, nonpulmonary sequential organ failure assessment score, respiratory rate at 1-2 hours of NIV, and PaO2/FiO2 at 1-2 hours of NIV has high accuracy to predict NIV failure among ARDS population.

Biosynthesis of a New Fusaoctaxin Virulence Factor in Fusarium graminearum Relies on a Distinct Path To Form a Guanidinoacetyl Starter Unit Priming Nonribosomal Octapeptidyl Assembly.

Fusarium graminearum is a pathogenic fungus causing huge economic losses worldwide via crop infection leading to yield reduction and grain contamination. The process through which the fungal invasion occurs remains poorly understood. We recently characterized fusaoctaxin A in F. graminearum, where this octapeptide virulence factor results from an assembly line encoded in fg3_54, a gene cluster proved to be involved in fungal pathogenicity and host adaptation. Focusing on genes in this cluster that are related to fungal invasiveness but not to the biosynthesis of fusaoctaxin A, we here report the identification and characterization of fusaoctaxin B, a new octapeptide virulence factor with comparable activity in wheat infection. Fusaoctaxin B differs from fusaoctaxin A at the N-terminus by possessing a guanidinoacetic acid (GAA) unit, formation of which depends on the combined activities of the protein products of fgm1-3. Fgm1 is a cytochrome P450 protein that oxygenates l-Arg to 4(R)-hydroxyl-l-Arg in a regio- and stereoselective manner. Then, Cß-Cγ bond cleavage proceeds in the presence of Fgm3, a pyridoxal-5'-phosphate-dependent lyase, giving guanidinoacetaldehyde and l-Ala. Rather than being directly oxidized to GAA, the guanidine-containing aldehyde undergoes spontaneous cyclization and subsequent enzymatic dehydrogenation to provide glycociamidine, which is linearized by Fgm2, a metallo-dependent amidohydrolase. The GAA path in F. graminearum is distinct from that previously known to involve l-Arg:l-Gly aminidotransferase activity. To provide this nonproteinogenic starter unit that primes nonribosomal octapeptidyl assembly, F. graminearum employs new chemistry to process l-Arg through inert C-H bond activation, selective C-C bond cleavage, cyclization-based alcohol dehydrogenation, and amidohydrolysis-associated linearization.

Correction: Characterization of a carboxyl methyltransferase in Fusarium graminearum provides insights into the biosynthesis of fusarin A.

Correction for 'Characterization of a carboxyl methyltransferase in Fusarium graminearum provides insights into the biosynthesis of fusarin A' by Qian Yang et al., Org. Biomol. Chem., 2021, DOI: 10.1039/d1ob01010g.

Characterization of a carboxyl methyltransferase in Fusarium graminearum provides insights into the biosynthesis of fusarin A.

Fusarium graminearum is a major fungal pathogen that causes a series of devastating crop diseases by producing a variety of mycotoxins. Fusarins are a class of polyketide-nonribosomal peptide hybrids. In Fusarium mycotoxins, a variable 2-pyrrolidone ring conjugates with a polyene chain substituted with a methyl ester moiety. The enzymatic route through which fusarin A, a major member of the fusarin family with a characteristic tetrohydrofuran-coupled pyrrolidone ring, is formed in F. graminearum has not been established. By targeting the final step in the biosynthesis of fusarin A, we report here an S-adenosyl methionine-dependent carboxyl methyltransferase responsible for the formation of the methyl ester moiety by in vivo gene inactivation, isolation and characterization of a key fusarin intermediate, and in vitro biochemical characterization. Related findings provide insights into the poorly understood biosynthetic pathway of fusarin A. Additionally, bioactivity assays demonstrate that the methyl ester is necessary for fusarin cytotoxicity.

Caerulomycin and collismycin antibiotics share a trans-acting flavoprotein-dependent assembly line for 2,2'-bipyridine formation.

Linear nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) template the modular biosynthesis of numerous nonribosomal peptides, polyketides and their hybrids through assembly line chemistry. This chemistry can be complex and highly varied, and thus challenges our understanding in NRPS and PKS-programmed, diverse biosynthetic processes using amino acid and carboxylate building blocks. Here, we report that caerulomycin and collismycin peptide-polyketide hybrid antibiotics share an assembly line that involves unusual NRPS activity to engage a trans-acting flavoprotein in C-C bond formation and heterocyclization during 2,2'-bipyridine formation. Simultaneously, this assembly line provides dethiolated and thiolated 2,2'-bipyridine intermediates through differential treatment of the sulfhydryl group arising from L-cysteine incorporation. Subsequent L-leucine extension, which does not contribute any atoms to either caerulomycins or collismycins, plays a key role in sulfur fate determination by selectively advancing one of the two 2,2'-bipyridine intermediates down a path to the final products with or without sulfur decoration. These findings further the appreciation of assembly line chemistry and will facilitate the development of related molecules using synthetic biology approaches.

Computational Investigation of the Mechanism of Diels-Alderase PyrI4.

We studied the mechanisms of activation and stereoselectivity of a monofunctional Diels-Alderase (PyrI4)-catalyzed intramolecular Diels-Alder reaction that leads to formation of the key spiro-tetramate moiety in the biosynthesis of the pyrroindomycin family of natural products. Key activation effects of PyrI4 include acid catalysis and an induced-fit mechanism that cooperate with the unique "lid" feature of PyrI4 to stabilize the Diels-Alder transition state. PyrI4 enhances the intrinsic Diels-Alder stereoselectivity of the substrate and leads to stereospecific formation of the product.

Long non-coding RNA TUG1 promotes airway remodelling by suppressing the miR-145-5p/DUSP6 axis in cigarette smoke-induced COPD.

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease that is primarily caused by cigarette smoke (CS)-induced chronic inflammation. In this study, we investigated the function and mechanism of action of the long non-coding RNA (lncRNA) taurine-up-regulated gene 1 (TUG1) in CS-induced COPD. We found that the expression of TUG1 was significantly higher in the sputum cells and lung tissues of patients with COPD as compared to that in non-smokers, and negatively correlated with the percentage of predicted forced expiratory volume in 1 second. In addition, up-regulation of TUG1 was observed in CS-exposed mice, and knockdown of TUG1 attenuated inflammation and airway remodelling in a mouse model. Moreover, TUG1 expression was higher in CS extract (CSE)-treated human bronchial epithelial cells and lung fibroblasts, whereas inhibition of TUG1 reversed CSE-induced inflammation and collagen deposition in vitro. Mechanistically, TUG1 promoted the expression of dual-specificity phosphatase 6 (DUSP6) by sponging miR-145-5p. DUSP6 overexpression reversed TUG1 knockdown-mediated inhibition of inflammation and airway remodelling. These findings suggested an important role of TUG1 in the pathological alterations associated with CS-mediated airway remodelling in COPD. Thus, TUG1 may be a promising therapeutic target in CS-induced airway inflammation and fibroblast activation.