An additional proofreader contributes to DNA replication fidelity in mycobacteria.

The removal of mis-incorporated nucleotides by proofreading activity ensures DNA replication fidelity. Whereas the ε-exonuclease DnaQ is a well-established proofreader in the model organism Escherichia coli, it has been shown that proofreading in a majority of bacteria relies on the polymerase and histidinol phosphatase (PHP) domain of replicative polymerase, despite the presence of a DnaQ homolog that is structurally and functionally distinct from E. coli DnaQ. However, the biological functions of this type of noncanonical DnaQ remain unclear. Here, we provide independent evidence that noncanonical DnaQ functions as an additional proofreader for mycobacteria. Using the mutation accumulation assay in combination with whole-genome sequencing, we showed that depletion of DnaQ in Mycolicibacterium smegmatis leads to an increased mutation rate, resulting in AT-biased mutagenesis and increased insertions/deletions in the homopolymer tract. Our results showed that mycobacterial DnaQ binds to the ß clamp and functions synergistically with the PHP domain proofreader to correct replication errors. Furthermore, the loss of dnaQ results in replication fork dysfunction, leading to attenuated growth and increased mutagenesis on subinhibitory fluoroquinolones potentially due to increased vulnerability to fork collapse. By analyzing the sequence polymorphism of dnaQ in clinical isolates of Mycobacterium tuberculosis (Mtb), we demonstrated that a naturally evolved DnaQ variant prevalent in Mtb lineage 4.3 may enable hypermutability and is associated with drug resistance. These results establish a coproofreading model and suggest a division of labor between DnaQ and PHP domain proofreader. This study also provides real-world evidence that a mutator-driven evolutionary pathway may exist during the adaptation of Mtb.

Blood serum levels of PACAP and migraine onset: A systematic review and meta-analysis of observational studies.

OBJECTIVE: We conducted a systematic review and meta-analysis to explore the relationship between blood pituitary adenylate cyclase-activating polypeptide (PACAP) levels and migraine. BACKGROUND: PACAP is involved in the onset of migraine, but the results from clinical studies on PACAP level variations across different periods of migraine are conflicting. METHODS: We systematically searched for observational studies that reported PACAP levels in people with migraine and non-migraine controls published in English from the PubMed, Web of Science, and Ovid electronic databases, or in Chinese from the Chinese National Knowledge Infrastructure and the WanFang Med database. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of the included studies. The quality of evidence for each outcome was assessed according to the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) guidelines. RESULTS: Of the 514 identified studies, 8 were eligible for inclusion. There was a "very low" level of evidence suggesting that the PACAP level is negatively correlated with migraine disease duration in adults with migraine (summary r = -0.35, 95% confidence interval [CI] -0.49 to -0.22) and that the PACAP is higher in people with migraine during the ictal period than in the interictal period (standardized mean difference = 0.41, 95% CI 0.17 to 0.66) for both adults and children with migraine. Adult patients with episodic migraine (weighted mean difference [WMD] = -9.58 pg/mL, 95% CI -13.41 to -5.75 pg/mL) or chronic migraine (WMD = -10.93 pg/mL, 95% CI -15.57 to -6.29 pg/mL) had lower blood PACAP levels than non-migraine controls during the interictal period, supported by a "low" or "very low" quality of evidence, respectively, according to the GRADE rules. CONCLUSION: There is a very low certainty of evidence suggesting that the PACAP level is negatively correlated with migraine disease duration of adults with migraine and it varies greatly among different periods of migraine of both adults and children with migraine.

Identifying sesterterpenoids via feature-based molecular networking and small-scale fermentation.

Terpenoids are known for their diverse structures and broad bioactivities with significant potential in pharmaceutical applications. However, natural products with low yields are usually ignored in traditional chemical analysis. Feature-based molecular networking (FBMN) was developed recently to cluster compounds with similar skeletons, which can highlight trace amounts of unknown compounds. Fusoxypene A is a sesterterpene synthesized by Fusarium oxysporum fusoxypene synthase (FoFS) with a unique 5/6/7/3/5 ring system. In this study, the FoFS-containing biosynthetic gene cluster was identified from F. oxysporum FO14005, and an efficient FBMN-based strategy was established to characterize four new sesterterpenoids, fusoxyordienoid A-D (1-4), based on a small-scale fermentation strategy. A cytochrome P450 monooxygenase, FusB, was found to be involved in the functionalization of fusoxypene A at C-17 and C-24 and responsible for the hydroxylation of fusoxyordienoid A at C-1 and C-8. This study highlights the potential of FBMN as a powerful tool for the discovery and characterization of natural compounds with low abundance. KEY POINTS: Combined small-scale fermentation and FBMN for rapid discovery of fusoxyordienoids Characterization of four new fusoxyordienoids with 5/6/7/3/5 ring system Biosynthetic pathway elucidation via tandem expression and substrate feeding.

Activating cryptic biosynthetic gene cluster through a CRISPR-Cas12a-mediated direct cloning approach.

Direct cloning of biosynthetic gene clusters (BGCs) from microbial genomes facilitates natural product-based drug discovery. Here, by combining Cas12a and the advanced features of bacterial artificial chromosome library construction, we developed a fast yet efficient in vitro platform for directly capturing large BGCs, named CAT-FISHING (CRISPR/Cas12a-mediated fast direct biosynthetic gene cluster cloning). As demonstrations, several large BGCs from different actinomycetal genomic DNA samples were efficiently captured by CAT-FISHING, the largest of which was 145 kb with 75% GC content. Furthermore, the directly cloned, 110 kb long, cryptic polyketide encoding BGC from Micromonospora sp. 181 was then heterologously expressed in a Streptomyces chassis. It turned out to be a new macrolactam compound, marinolactam A, which showed promising anticancer activity. Our results indicate that CAT-FISHING is a powerful method for complicated BGC cloning, and we believe that it would be an important asset to the entire community of natural product-based drug discovery.

Chrysomycins, Anti-Tuberculosis C-Glycoside Polyketides from Streptomyces sp. MS751.

A new dimeric C-glycoside polyketide chrysomycin F (1), along with four new monomeric compounds, chrysomycins G (2), H (3), I (4), J (5), as well as three known analogues, chrysomycins A (6), B (7), and C (8), were isolated and characterised from a strain of Streptomyces sp. obtained from a sediment sample collected from the South China Sea. Their structures were determined by detailed spectroscopic analysis. Chrysomycin F contains two diastereomers, whose structures were further elucidated by a biomimetic [2 + 2] photodimerisation of chrysomycin A. Chrysomycins B and C showed potent anti-tuberculosis activity against both wild-type Mycobacterium tuberculosis and a number of clinically isolated MDR M. tuberculosis strains.

Nanometer-resolution in situ structure of the SARS-CoV-2 postfusion spike protein.

The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mediates membrane fusion to allow entry of the viral genome into host cells. To understand its detailed entry mechanism and develop a specific entry inhibitor, in situ structural information on the SARS-CoV-2 spike protein in different states is urgent. Here, by using cryo-electron tomography, we observed both prefusion and postfusion spikes in ß-propiolactone-inactivated SARS-CoV-2 virions and solved the in situ structure of the postfusion spike at nanometer resolution. Compared to previous reports, the six-helix bundle fusion core, the glycosylation sites, and the location of the transmembrane domain were clearly resolved. We observed oligomerization patterns of the spikes on the viral membrane, likely suggesting a mechanism of fusion pore formation.

Comparative efficacy and safety of different pharmacological therapies to medication overuse headache: a network meta-analysis.

BACKGROUND: Controversy exists whether prophylactic drugs are necessary in the treatment of medication overuse headache (MOH). OBJECTIVES: To determine comparative benefits and safety of available drugs for the treatment of MOH including elimination of medication overuse (MO). METHODS: We systematically reviewed randomized controlled trials though an extensive literature search comparing different drug effects on MOH. A random-effect network meta-analysis was conducted to rank comparative effects of interventions. Outcome improvements from baseline include responder rate defined as ≥ 50% reduction of headache frequency, proportion of patients who revert to no acute medication overuse (nMO), and reduction in monthly headache and acute medication intake frequency. Certainty of evidence was classified using the Grading of Recommendations, Assessment, Development & Evaluation (GRADE). RESULTS: Of 8,248 screened publications, 28 were eligible for analysis. Topiramate was found to be beneficial based on its responder rate (odds ratios [OR] 4.93), headache frequency (weighted mean difference [WMD] -5.53) and acute medication intake frequency (WMD - 6.95), with fewer safety issues (i.e., tolerability, or more adverse events) than placebo (OR 0.20). Fremanezumab, galcanezumab and botulinum toxin type A (BTA) were beneficial for increased responder rates (OR 3.46 to 3.07, 2.95, and 2.57, respectively). For reversion to nMO, eptinezumab, fremanezumab and BTA were superior to placebo (OR 2.75 to 2.64, 1.87 to1.57, and 1.55, respectively). Eptinezumab, fremanezumab, erenumab 140 mg, and BTA were more efficacious than erenumab 70 mg (OR 3.84 to 3.70, 2.60 to 2.49, 2.44 and 2.16, respectively) without differences in safety and tolerability. CONCLUSION: Despite lower safety and greater intolerability issues, topiramate has large beneficial effects probably on increasing responder rates, reducing headache frequency, and might reduce monthly medication intake frequency. Fremanezumab, galcanezumab, and eptinezumab are promising for increasing responder rates. For reversion to nMO, eptinezumab has large beneficial effects, fremanezumab has a smaller effect. BTA might have a moderate effect on responder rates and probably has a small effect on reversion to nMO. TRIAL REGISTRATION: PROSPERO, CRD42021193370.

Function Switch of a Fungal Sesterterpene Synthase through Molecular Dynamics Simulation Assisted Alteration of an Aromatic Residue Cluster in the Active Pocket of PfNS.

Terpene synthases (TPSs) play pivotal roles in generating diverse terpenoids through complex cyclization pathways. Protein engineering of TPSs offers a crucial approach to expanding terpene diversity. However, significant potential remains untapped due to limited understanding of the structure-function relationships of TPSs. In this investigation, using a joint approach of molecular dynamics simulations-assisted engineering and site-directed mutagenesis, we manipulated the aromatic residue cluster (ARC) of a bifunctional terpene synthase (BFTPS), Pestalotiopsis fici nigtetraene synthase (PfNS). This led to the discovery of previously unreported catalytic functions yielding different cyclization patterns of sesterterpenes. Specifically, a quadruple variant (F89A/Y113F/W193L/T194W) completely altered PfNS's function, converting it from producing the bicyclic sesterterpene nigtetraene to the tricyclic ophiobolin F. Additionally, analysis of catalytic profiles by double, triple, and quadruple variants demonstrated that the ARC functions as a switch, unprecedently redirecting the production of 5/11 bicyclic (Type B) sesterterpenes to 5/15 bicyclic (Type A) ones. Molecular dynamics simulations and theozyme calculations further elucidated that, in addition to cation-π interactions, C-H⋅⋅⋅π interactions also play a key role in the cyclization patterns. This study offers a feasible strategy in protein engineering of TPSs for various industrial applications.

Biosynthesis of 4-Acyl-5-aminoimidazole Alkaloids Featuring a New Friedel-Crafts Acyltransferase.

Friedel-Crafts acylation (FCA) is a highly beneficial approach in organic chemistry for creating the important C-C bonds that are necessary for building intricate frameworks between aromatic substrates and an acyl group. However, there are few reports about enzyme catalyzed FCA reactions. In this study, 4-acyl-5-aminoimidazole alkaloids (AAIAs), streptimidazoles A-C (1-3), and the enantiopure (+)-nocarimidazole C (4) as well as their ribosides, streptimidazolesides A-D (5-8), were identified from the fermentation broth of Streptomyces sp. OUCMDZ-944 or heterologous S. coelicolor M1154 mutant. The biosynthetic gene cluster (smz) was identified, and the biosynthetic pathway of AAIAs was elucidated for the first time. In vivo and in vitro studies proved the catalytic activity of the four essential genes smzB, -C, -E, and -F for AAIAs biosynthesis and clarified the biosynthetic process of the alkaloids. The ligase SmzE activates fatty acyl groups and connects them to the acyl carrier protein (ACP) holo-SmzF. Then, the acyl group is transferred onto the key residue Cys49 of SmzB, a new Friedel-Crafts acyltransferase (FCase). Subsequently, the FCA reaction between the acyl groups and 5-aminoimidazole ribonucleotide (AIR) occurs to generate the key intermediate AAIA-nucleotides catalyzed by SmzB. Finally, the hydrolase SmzC catalyzes the N-glycosidic bond cleavage of the intermediates to form AAIAs. Structural simulation, molecular modeling, and mutational analysis of SmzB showed that Tyr26, Cys49, and Tyr93 are the key catalytic residues in the C-C bond formation of the acyl chain of AAIAs, providing mechanistic insights into the enzymatic FCA reaction.

Molecular Insights into the Improved Bioactivity of Interferon Conjugates Attached to a Helical Polyglutamate.

Attaching polymers, especially polyethylene glycol (PEG), to protein drugs has emerged as a successful strategy to prolong circulation time in the bloodstream. The hypothesis is that the flexible chain wobbles on the protein's surface, thus resisting potential nonspecific adsorption. Such a theoretical framework may be challenged when a helical polyglutamate is used to conjugate with target proteins. In this study, we investigated the structure-activity relationships of polyglutamate-interferon conjugates P(EG3Glu)-IFN using molecular simulations. Our results show that the local crowding effect induced by oligoethylene glycols (i.e., EG3) is the primary driving force for helix formation in P(EG3Glu), and its helicity can be effectively increased by reducing the free volume of the two termini. Furthermore, it was found that the steric hindrance induced by IFN is not conductive to the helicity of P(EG3Glu) but contributes to its dominant orientation relative to interferon. The orientation of IFN relative to the helical P(EG3Glu) can help to protect the protein drug from neutralizing antibodies while maintaining its bioactivity. These findings suggest that the helical structure and its orientation are critical factors to consider when updating the theoretical framework for protein-polymer conjugates.

Correspondence on "Structural Insight into the Catalytic Mechanism of the Endoperoxide Synthase FtmOx1".

In their recent Angewandte Chemie publication (doi: 10.1002/anie.202112063), Cen, Wang, Zhou et al. reported the crystal structure of a ternary complex of the non-heme iron endoperoxidase FtmOx1 (PDB entry 7ETK). The biochemical data assessed in this study were from a retracted study (doi: 10.1038/nature15519) by Zhang, Liu, Zhang et al.; no additional biochemical data were included, yet there was no discussion on the source of the biochemical data in the report by Cen, Wang, Zhou et al. Based on this new crystal structure and subsequent QM/MM-MD calculations, Cen, Wang, Zhou et al. concluded that their work provided evidence supporting the CarC-like mechanistic model for FtmOx1 catalysis. However, the authors did not accurately describe either the CarC-like model or the COX-like model, and they did not address the differences between them. Further, and contrary to their interpretations in the manuscript, the authors' data are consistent with the COX-like model once the details of the CarC-like and COX-like models have been carefully analyzed.

Sequence Effect of Peptide-Based Materials on Delivering Interferon-α (IFN-α): A Molecular Dynamic Perspective.

Peptide-based biomaterials exhibit great potentials in developing drug delivery platforms due to their biocompatibility and biodegradability beyond poly(ethylene glycol). How different amino acids in peptides used for delivery play their roles is still unclear at the microscopic level. This work compared the assembly behaviors of a series of peptides around interferon-α (IFN-α). Through all-atom molecular simulations, the sequence effect of peptides on delivering interferon-α was quantitively characterized. The hydrophobic elastin-like peptide (VPGAG)n preferred to self-aggregate into dense clusters, rather than encapsulate IFN-α. The hydrophilic zwitterionic peptides with repeating unit "KE" tended to phase-separate from IFN-α in the mixture. In contrast, peptides with a hybrid sequence, i.e., (VPKEG)n, exhibited the highest contact preference, and the formed protective shell endowed IFN-α with better thermal stability and stealth property and achieved a subtle balance between protecting IFN-α and subsequent releasing. Further energy decomposition analysis revealed that the positively charged Lys contributed most to the binding affinity while the negatively charged Glu contributed most to the hydrophilic property of peptide-based materials. In summary, this article reveals why peptides composed of repeating hydrophobic and charged residues could be a potential choice for delivering therapeutic proteins in the form of solution.

Schultriene and nigtetraene: two sesterterpenes characterized from pathogenetic fungi via genome mining approach.

Fungal bifunctional terpene synthases (BFTSs) have been reported to contribute to the biosynthesis of a variety of di/sesterterpenes via different carbocation transportation pathways. Genome mining of new BFTSs from unique fungal resources will, theoretically, allow for the identification of new terpenes. In this study, we surveyed the distribution of BFTSs in our in-house collection of 430 pathogenetic fungi and preferred two BFTSs (CsSS and NnNS), long distance from previously characterized BFTSs and located in relatively independent branches, based on the established phylogenetic tree. The heterologous expression of the two BFTSs in Aspergillus oryzae and Saccharomyces cerevisiae led to the identification of two new sesterterpenes separately, 5/12/5 tricyclic type-A sesterterpene (schultriene, 1) for CsSS and 5/11 bicyclic type-B sesterterpene (nigtetraene, 2) for NnNS. In addition, to the best of our knowledge, 2 is the first 5/11 bicyclic type-B characterized sesterterpene to date. On the basis of this, the plausible cyclization mechanisms of 1 and 2 were proposed based on density functional theory calculations. These new enzymes and their corresponding terpenes suggest that the chemical spaces produced by BFTSs remain large and also provide important evidences for further protein engineering for new terpenes and for understanding of cyclization mechanism catalyzed by BFTSs. KEY POINTS: • Genome mining of two BFTSs yields two new sesterterpenoids correspondingly. • Identification of the first 5/11 ring system type-B product. • Parse out the rational cyclization mechanism of isolated sesterterpenoids.

Antibacterial polyene-polyol macrolides and cyclic peptides from the marine-derived Streptomyces sp. MS110128.

Marine microbes provide an important resource to discover new chemical compounds with biological activities beneficial to drug discovery. In our study, two new polyene macrolides, pyranpolyenolides A (1) and B (2), and one new natural cyclic peptide (9), together with two known polyenes (7 and 8) and three known cyclic peptides (10-12), were isolated from a culture of the marine Streptomyces sp. MS110128. In addition, four new polyene macrolides, pyranpolyenolides C-F (3-6), were identified as olefin geometric isomers that were most likely produced by photochemical conversion during the cultivation or isolation procedures. The pyranpolyenolides are 32-membered macrolides endowed with a conjugated tetraene and several pairs of 1,3-dihydroxyl groups. Pyranpolyenolides that contain a hydropyran group have not been previously reported. Four cyclic peptides (9-12) showed significant activities against Bacillus subtilis, Staphylococcus aureus, and methicillin-resistant S. aureus with supporting MIC values ranging from 0.025 to 1.25 µg/mL. These cyclic peptides containing piperazic moieties showed moderate activities with MIC values of 12.5 µg/mL against Bacille Calmette Guerin (BCG), an attenuated form of the bovine. Additionally, cyclic peptide 12 showed moderate antifungal activity against Candida albicans with an MIC value of 12.5 µg/mL. KEY POINTS: • Discovery of new polyenes and cyclic peptides from a marine-derived Actinomycete. • Cyclic peptides containing piperazic moieties exhibited good antibacterial activity.

Genome-guided investigation of anti-inflammatory sesterterpenoids with 5-15 trans-fused ring system from phytopathogenic fungi.

Fungal terpenoids catalyzed by bifunctional terpene synthases (BFTSs) possess interesting bioactive and chemical properties. In this study, an integrated approach of genome mining, heterologous expression, and in vitro enzymatic activity assay was used, and these identified a unique BFTS sub-clade critical to the formation of a 5-15 trans-fused bicyclic sesterterpene preterpestacin I (1). The 5-15 bicyclic BFTS gene clusters were highly conserved but showed relatively wide phylogenetic distribution across several species of the diverged fungal classes Dothideomycetes and Sordariomycetes. Further genomic organization analysis of these homologous biosynthetic gene clusters from this clade revealed a glycosyltransferase from the graminaceous pathogen Bipolaris sorokiniana isolate BS11134, which was absent in other 5-15 bicyclic BFTS gene clusters. Targeted isolation guided by BFTS gene deletion led to the identification of two new sesterterpenoids (4, and 6) from BS11134. Compounds 2 and 4 showed moderate effects on LPS-induced nitrous oxide production in the murine macrophage-like cell line RAW264.7 with in vitro inhibition rates of 36.6 ± 2.4% and 24.9 ± 2.1% at 10 µM, respectively. The plausible biosynthetic pathway of these identified compounds was proposed as well. This work revealed that phytopathogenic fungi can serve as important sources of active terpenoids via systematic analysis of the genomic organization of BFTS biosynthetic gene clusters, their phylogenetic distribution in fungi, and cyclization properties of their metabolic products. KEY POINTS: • Genome mining of the first BFTS BGC harboring a glycosyltransferase. • Gene-deletion guided isolation revealed three novel 5-15 bicyclic sesterterpenoids. • Biosynthetic pathway of isolated sesterterpenoids was proposed.

The Unusual Homodimer of a Heme-Copper Terminal Oxidase Allows Itself to Utilize Two Electron Donors.

The heme-copper oxidase superfamily comprises cytochrome c and ubiquinol oxidases. These enzymes catalyze the transfer of electrons from different electron donors onto molecular oxygen. A B-family cytochrome c oxidase from the hyperthermophilic bacterium Aquifex aeolicus was discovered previously to be able to use both cytochrome c and naphthoquinol as electron donors. Its molecular mechanism as well as the evolutionary significance are yet unknown. Here we solved its 3.4 Šresolution electron cryo-microscopic structure and discovered a novel dimeric structure mediated by subunit I (CoxA2) that would be essential for naphthoquinol binding and oxidation. The unique structural features in both proton and oxygen pathways suggest an evolutionary adaptation of this oxidase to its hyperthermophilic environment. Our results add a new conceptual understanding of structural variation of cytochrome c oxidases in different species.

Deciphering the Biosynthesis of TDP-ß-l-oleandrose in Avermectin.

Avermectin (AVM) refers to eight macrolides containing a common l-oleandrosyl disaccharide chain indispensable to their antiparasitic bioactivities. We delineated the biosynthetic pathway of TDP-ß-l-oleandrose (1), the sugar donor of AVM, by characterizing AveBVIII, AveBV, and AveBVII as TDP-sugar 3-ketoreductase, 5-epimerase, and 3-O-methyltransferase, respectively. On the basis of this pathway, we successfully reconstituted the biosynthesis of 1 in Escherichia coli. Our work completes the biosynthetic pathway of AVM and lays a solid foundation for further studies.

A new abyssomicin polyketide with anti-influenza A virus activity from a marine-derived Verrucosispora sp. MS100137.

Marine microorganisms live in dramatically different environments and have attracted much attention for their structurally unique natural products with potential strong biological activity. Based on the one strain-many compounds (OSMAC) strategy and liquid chromatography mass spectrometry (LC-MS) methods, our continuing efforts on the investigation of novel active compounds from marine Verrucosispora sp. MS100137 has led to the identification of a new polycyclic metabolite, abyssomicin Y (1), together with six known abyssomicin and proximicin analogs (2-7). Abyssomicin Y is a type I abyssomicin with an epoxide group at C-8 and C-9. Compounds 1-3 showed potent inhibitory effects against the influenza A virus; their observed inhibition rates were 97.9%, 98.3%, and 95.9%, respectively, at a concentration of 10 µM, and they displayed lower cytotoxicity than 4. The structures were determined by different NMR techniques and HRMS experiments. This investigation revealed that OSMAC could serve as a useful method for enabling the activation of the silent genes in the microorganism and for the formation of previously unreported active secondary metabolites.

Genome-based mining of new antimicrobial meroterpenoids from the phytopathogenic fungus Bipolaris sorokiniana strain 11134.

Polyketide-terpenoid hybrid compounds are one of the largest families of meroterpenoids, with great potential for drug development for resistant pathogens. Genome sequence analysis of secondary metabolite gene clusters of a phytopathogenic fungus, Bipolaris sorokiniana 11134, revealed a type I polyketide gene cluster, consisting of highly reducing polyketide synthase, non-reducing polyketide synthase, and adjacent prenyltransferase. MS- and UV-guided isolations led to the isolation of ten meroterpenoids, including two new compounds: 19-dehydroxyl-3-epi-arthripenoid A (1) and 12-keto-cochlioquinone A (2). The structures of 1-10 were elucidated by the analysis of NMR and high-resolution electrospray ionization mass spectroscopy data. Compounds 5-8 and 10 showed moderate activity against common Staphylococcus aureus and methicillin-resistant S. aureus, with minimum inhibitory concentration (MIC) values of 12.5-100 µg/mL. Compound 5 also exhibited activity against four clinical resistant S. aureus strains and synergistic antifungal activity against Candida albicans with MIC values of 12.5-25 µg/mL. The biosynthetic gene cluster of the isolated compounds and their putative biosynthetic pathway are also proposed. KEY POINTS: • Ten meroterpenoids were identified from B. sorokiniana, including two new compounds. • Cochlioquinone B (5) showed activity against MRSA and synergistic activity against C. albicans. • The biosynthetic gene cluster and biosynthetic pathway of meroterpenoids are proposed. • Genome mining provided a new direction to uncover the diversity of meroterpenoids.

A 3.3†Å-Resolution Structure of Hyperthermophilic Respiratory Complex†III Reveals the Mechanism of Its Thermal Stability.

Respiratory chain complexes convert energy by coupling electron flow to transmembrane proton translocation. Owing to a lack of atomic structures of cytochrome bc1 complex (Complex III) from thermophilic bacteria, little is known about the adaptations of this macromolecular machine to hyperthermophilic environments. In this study, we purified the cytochrome bc1 complex of Aquifex aeolicus, one of the most extreme thermophilic bacteria known, and determined its structure with and without an inhibitor at 3.3 Šresolution. Several residues unique for thermophilic bacteria were detected that provide additional stabilization for the structure. An extra transmembrane helix at the N-terminus of cyt. c1 was found to greatly enhance the interaction between cyt. b and cyt. c1 , and to bind a phospholipid molecule to stabilize the complex in the membrane. These results provide the structural basis for the hyperstability of the cytochrome bc1 complex in an extreme thermal environment.