Structural and mechanistic investigations on CC bond forming α-oxoamine synthase allowing L-glutamate as substrate.

Carbon­carbon (C-C) bonds serve as the fundamental structural backbone of organic molecules. As a critical CC bond forming enzyme, α-oxoamine synthase is responsible for the synthesis of α-amino ketones by performing the condensation reaction between amino acids and acyl-CoAs. We previously identified an α-oxoamine synthase (AOS), named as Alb29, involved in albogrisin biosynthesis in Streptomyces albogriseolus MGR072. This enzyme belongs to the α-oxoamine synthase family, a subfamily under the pyridoxal 5'-phosphate (PLP) dependent enzyme superfamily. In this study, we report the crystal structures of Alb29 bound to PLP and L-Glu, which provide the atomic-level structural insights into the substrate recognition by Alb29. We discover that Alb29 can catalyze the amino transformation from L-Gln to L-Glu, besides the condensation of L-Glu with ß-methylcrotonyl coenzyme A. Subsequent structural analysis has revealed that one flexible loop in Alb29 plays an important role in both amino transformation and condensation. Based on the crystal structure of the S87G mutant in the loop region, we capture two distinct conformations of the flexible loop in the active site, compared with the wild-type Alb29. Our study offers valuable insights into the catalytic mechanism underlying substrate recognition of Alb29.

Identification of an α-Oxoamine Synthase and a One-Pot Two-Step Enzymatic Synthesis of α-Amino Ketones.

Alb29, an α-oxoamine synthase involved in albogrisin biosynthesis in Streptomyces albogriseolus MGR072, was characterized and responsible for the incorporation of l-glutamate to acyl-coenzyme A substrates. Combined with Alb29 and Mgr36 (an acyl-coenzyme A ligase), a one-pot enzymatic system was established to synthesize seven α-amino ketones. When these α-amino ketones were fed into the alb29 knockout strain Δalb29, respectively, the albogrisin analogs with different side chains were observed.

Constructing Microbial Hosts for the Production of Benzoheterocyclic Derivatives.

Natural products containing benzoheterocyclic skeletons are widely found in plants and exhibit various pharmacological activities. To address the current limited availability of these compounds, we herein demonstrate the production of benzopyran, furanocoumarins, and pyranocoumarins in Streptomyces xiamenensis by employing prenyltransferases and two substrate-promiscuous enzymes, XimD and XimE. To avoid the degradation in S. xiamenensis, furanocoumarins and pyranocoumarins were also successfully produced in Escherichia coli. The production of linear furanocoumarins (marmesin) and angular pyranocoumarins (decursinol) reached 3.6 and 3.7 mg/L in shake flasks, respectively. To the best of our knowledge, this is the first report of the microbial production of the plant metabolites furanocoumarins and pyranocoumarins. Our study complements the missing link in the biosynthesis of pyranocoumarins by leveraging the catalytic promiscuity of microbial enzymes.

Ikarugamycin inhibits pancreatic cancer cell glycolysis by targeting hexokinase 2.

Mangrove-derived actinobacteria strains are well-known for producing novel secondary metabolites. The polycyclic tetramate macrolactam (PTM), ikarugamycin (IKA) isolated from Streptomyces xiamenensis 318, exhibits antiproliferative activities against pancreatic ductal adenocarcinoma (PDAC) in vitro. However, the protein target for bioactive IKA is unclear. In this study, whole transcriptome-based profiling revealed that the glycolysis pathway is significantly affected by IKA. Metabolomic studies demonstrated that IKA treatment induces a significant drop in glucose-6-phosphate and a slight increase in intracellular glucose level. Analysis of glucose consumption, lactate production, and the extracellular acidification rate confirmed the inhibitory role of IKA on the glycolytic flux in PDAC cells. Surface plasmon resonance (SPR) experiments and docking studies identified the key enzyme of glycolysis, hexokinase 2 (HK2), as a molecular target of IKA. Moreover, IKA reduced tumor size without overt cytotoxicity in mice with PDAC xenografts and increased chemotherapy response to gemcitabine in PDAC cells in vitro. Taken together, IKA can block glycolysis in pancreatic cancer by targeting HK2, which may be a potential drug candidate for PDAC treatment.

Three transcriptional regulators positively regulate the biosynthesis of polycyclic tetramate macrolactams in Streptomyces xiamenensis 318.

Polycyclic tetramate macrolactams (PTMs) are a widely distributed class of structurally complex natural products, and most of them exhibit multiple biological activities. However, the transcriptional regulators (TRs) involved in the regulation of PTM production have seldom been reported. Here, we identified three TRs, i.e., Sxim_22880, CvnABCSx, and WblASx, and revealed their positive roles in the regulation of PTM biosynthesis in mangrove-derived Streptomyces xiamenensis 318. This strain produces a considerable amount of PTMs at 30 °C, but the production of PTMs is mostly blocked at 37 °C. Quantitative real-time PCR analysis confirmed that the transcriptions of PTM biosynthetic genes were downregulated. We determined that the transcriptions of several putative TRs, i.e., WblASx, Sxim_22880, and CvnCSx, were significantly downregulated under such heat-shock conditions. We showed that the transcription of PTM biosynthetic genes and the production of PTMs could be restored at 37 °C if the impaired transcriptions of wblASx, sxim_22880, and cvnABCSx were restored. Electrophoretic mobility shift assays showed that none of these TRs could bind to the promoter region of the PTM gene cluster, suggesting their indirect but positive involvement in the regulation on PTM production. Moreover, concurrent overexpression of the three TRs in S. xiamenensis 318 resulted in a 242.5% increase in PTM production when the strain was cultured at 30 °C. Furthermore, overexpression of these three TRs in Streptomyces sp. FR-008 and S. albus J1074 stimulated the production of new secondary metabolites, indicating that these conserved TRs could be used to activate cryptic secondary metabolite gene clusters in Streptomyces.

New alkylated benzoquinones from mangrove plant Aegiceras corniculatum with anticancer activity.

Three new alkylated benzoquinones, 2-hydroxy-5-ethoxy-3-nonyl-1,4-benzoquinone (1), 5-O-butyl-embelin (2), and 2,5-dihydroxy-6-methyl-3-pentadecyl-1,4-benzoquinone (3), together with seven known analogues (4-10), were isolated from the stems and twigs of mangrove plant, Aegiceras corniculatum. Their structural elucidation was achieved by spectroscopic methods, chemical exchanging experiments, and semisynthesis method. The cytotoxic activities of all the isolated compounds were evaluated by MTT assay. Compounds 1, 2, 8, 9, and 10 possess varying degrees of selective cytotoxicity against HL-60, HepG2, BGC-823, and A2780 cell lines.[Formula: see text].

Rational engineering of amide synthetase enables bioconversion to diverse xiamenmycin derivatives.

XimA is a unique amide synthetase that belongs to the ANL superfamily of adenylating enzymes, but with a special structural fold. In order to improve the enzyme promiscuity, we engineered XimA by site-directed mutagenesis at a specific position based on our theoretical model of XimA. Thus, we were able to produce diverse benzopyran derivatives with up to 15 different l-form and d-form amino acid substitutions, catalyzed by several XimA variants. Molecular docking and molecular dynamics simulations conducted for various XimA systems provide further structural insights into the substitution effects of the phenylalanine-201 as an active site residue on protein dynamics and enzyme catalysis.

Characterization and Nonenzymatic Transformation of Three Types of Alkaloids from Streptomyces albogriseolus MGR072 and Discovery of Inhibitors of Indoleamine 2,3-Dioxygenase.

The known benzonaphthyridine alkaloid, albogrisin A (1), and six new compounds, including two pyrazinone stereoisomers, albogrisin B (2)/B' (2'), together with four 4H-pyrroloquinolinones, two diastereoisomers, albogrisin C (3)/C' (3'), and their methyl esters, albogrisin D (4)/D' (4'), were isolated from mangrove-derived Streptomyces albogriseolus MGR072. 2 and 2' are converted into 1 in acidic aqueous solution but into 3/3' and 4/4' in 0.05% trifluoroacetic acid acetonitrile. 4 and 4' are new indoleamine 2,3-dioxygenase 1 inhibitors.

Correction to: 'Dynamical modelling of secondary metabolism and metabolic switches in Streptomyces xiamenensis 318'.

[This corrects the article DOI: 10.1098/rsos.190418.].

Dynamical modelling of secondary metabolism and metabolic switches in Streptomyces xiamenensis 318.

The production of secondary metabolites, while important for bioengineering purposes, presents a paradox in itself. Though widely existing in plants and bacteria, they have no definite physiological roles. Yet in both native habitats and laboratories, their production appears robust and follows apparent metabolic switches. We show in this work that the enzyme-catalysed process may improve the metabolic stability of the cells. The latter can be responsible for the overall metabolic behaviours such as dynamic metabolic landscape, metabolic switches and robustness, which can in turn affect the genetic formation of the organism in question. Mangrove-derived Streptomyces xiamenensis 318, with a relatively compact genome for secondary metabolism, is used as a model organism in our investigation. Integrated studies via kinetic metabolic modelling, transcriptase measurements and metabolic profiling were performed on this strain. Our results demonstrate that the secondary metabolites increase the metabolic fitness of the organism via stabilizing the underlying metabolic network. And the fluxes directing to NADH, NADPH, acetyl-CoA and glutamate provide the key switches for the overall and secondary metabolism. The information may be helpful for improving the xiamenmycin production on the strain.