Alteration of the Route to Menaquinone towards Isochorismate-Derived Metabolites

Rutinosides-derived from Sarocladium strictum 6-O-α-rhamnosyl-β-glucosidase show enhanced anti-tumoral activity in pancreatic cancer cells

BACKGROUND

Low targeting efficacy and high toxicity continue to be challenges in Oncology. A promising strategy is the glycosylation of chemotherapeutic agents to improve their pharmacodynamics and anti-tumoral activity. Herein, we provide evidence of a novel approach using diglycosidases from fungi of the Hypocreales order to obtain novel rutinose-conjugates therapeutic agents with enhanced anti-tumoral capacity.

RESULTS

Screening for diglycosidase activity in twenty-eight strains of the genetically related genera Acremonium and Sarocladium identified 6-O-α-rhamnosyl-β-glucosidase (αRβG) of Sarocladium strictum DMic 093557 as candidate enzyme for our studies. Biochemically characterization shows that αRβG has the ability to transglycosylate bulky OH-acceptors, including bioactive compounds. Interestingly, rutinoside-derivatives of phloroglucinol (PR) resorcinol (RR) and 4-methylumbelliferone (4MUR) displayed higher growth inhibitory activity on pancreatic cancer cells than the respective aglycones without significant affecting normal pancreatic epithelial cells. PR exhibited the highest efficacy with an IC50 of 0.89 mM, followed by RR with an IC50 of 1.67 mM, and 4MUR with an IC50 of 2.4 mM, whereas the respective aglycones displayed higher IC50 values: 4.69 mM for phloroglucinol, 5.90 mM for resorcinol, and 4.8 mM for 4-methylumbelliferone. Further, glycoconjugates significantly sensitized pancreatic cancer cells to the standard of care chemotherapy agent gemcitabine.

CONCLUSIONS

αRβG from S. strictum transglycosylate-based approach to synthesize rutinosides represents a suitable option to enhance the anti-proliferative effect of bioactive compounds. This finding opens up new possibilities for developing more effective therapies for pancreatic cancer and other solid malignancies.

Biosynthesis of Menaquinone in E. coli: Identification of an Elusive Isomer of SEPHCHC

In the biosynthesis of menaquinone in bacteria, the thiamine diphosphate-dependent enzyme MenD catalyzes the decarboxylative carboligation of α-ketoglutarate and isochorismate to (1R,2S,5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC). The regioisomer of SEPHCHC, namely (1R,5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-2-ene-1-carboxylate (iso-SEPHCHC), has been considered as a possible product, however, its existence has been doubtful due to a spontaneous elimination of pyruvate from SEPHCHC to 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate (SHCHC). In this work, the regioisomer iso-SEPHCHC was distinguished from SEPHCHC by liquid chromatography-tandem mass spectrometry. Iso-SEPHCHC was purified and identified by NMR spectroscopy. Just as SEPHCHC remained hidden as a MenD product for more than two decades, its regioisomer iso-SEPHCHC has remained until now.

Targeted accumulation of selective anticancer depsipeptides by reconstructing the precursor supply in the neoantimycin biosynthetic pathway

BACKGROUND

Neoantimycins are a group of 15-membered ring depsipeptides isolated from Streptomycetes with a broad-spectrum of anticancer activities. Neoantimycin biosynthesis is directed by the hybrid multimodular megaenzymes of non-ribosomal peptide synthetase and polyketide synthase. We previously discovered a new neoantimycin analogue unantimycin B, which was demonstrated to have selective anticancer activities and was produced from the neoantimycin biosynthetic pathway with a starter unit of 3-hydroxybenzoate, instead of the 3-formamidosalicylate unit that is common for neoantimycins. However, the low fermentation titre and tough isolation procedure have hindered in-depth pharmacological investigation of unantimycin B as an anticancer agent.

RESULTS

In this work, we genetically constructed two unantimycin B producer strains and inhibited neoantimycins production by removing natO and natJ-L genes essential for 3-formamidosalicylate biosynthesis, therefore facilitating chromatographic separation of unantimycin B from the complex fermentation extract. Based on the ΔnatO mutant, we improved unantimycin B production twofold, reaching approximately 12.8 mg/L, by feeding 3-hydroxybenzoate during fermentation. Furthermore, the production was improved more than sixfold, reaching approximately 40.0 mg/L, in the ΔnatO strain introduced with a chorismatase gene highly expressed under a strong promoter for endogenously over-producing 3-hydroxybenzoate.

CONCLUSION

This work provides a case of targeting accumulation and significant production improvement of medicinally interesting natural products via genetic manipulation of precursor biosynthesis in Streptomycetes, the talented producers of pharmaceutical molecules.

Chorismate- and isochorismate converting enzymes: versatile catalysts acting on an important metabolic node

Chorismate and isochorismate represent an important branching point connecting primary and secondary metabolism in bacteria, fungi, archaea and plants. Chorismate- and isochorismate-converting enzymes are potential targets for new bioactive compounds, as well as valuable biocatalysts for the in vivo and in vitro synthesis of fine chemicals. The diversity of the products of chorismate- and isochorismate-converting enzymes is reflected in the enzymatic three-dimensional structures and molecular mechanisms. Due to the high reactivity of chorismate and its derivatives, these enzymes have evolved to be accurately tailored to their respective reaction; at the same time, many of them exhibit a fascinating flexibility regarding side reactions and acceptance of alternative substrates. Here, we give an overview of the different (sub)families of chorismate- and isochorismate-converting enzymes, their molecular mechanisms, and three-dimensional structures. In addition, we highlight important results of mutagenetic approaches that generate a broader understanding of the influence of distinct active site residues for product formation and the conversion of one subfamily into another. Based on this, we discuss to what extent the recent advances in the field might influence the general mechanistic understanding of chorismate- and isochorismate-converting enzymes. Recent discoveries of new chorismate-derived products and pathways, as well as biocatalytic conversions of non-physiological substrates, highlight how this vast field is expected to continue developing in the future.

Advances in menaquinone biosynthesis: sublocalisation and allosteric regulation

Menaquinones (vitamin K2) are a family of redox-active small molecules with critical functions across all domains of life, including energy generation in bacteria and bone health in humans. The enzymes involved in menaquinone biosynthesis also have bioengineering applications and are potential antimicrobial drug targets. New insights into the essential roles of menaquinones, and their potential to cause redox-related toxicity, have highlighted the need for this pathway to be tightly controlled. Here, we provide an overview of our current understanding of the classical menaquinone biosynthesis pathway in bacteria. We also review recent discoveries on protein-level allostery and sublocalisation of membrane-bound enzymes that have provided insight into the regulation of flux through this biosynthetic pathway.

A chemical screening method for menaquinone-producing strains based on HPLC-UV technology

Despite menaquinones (MKs)-4 and - 7 being known to have extensive biological activities and applications, less attention has been paid to the other MKs. Thus, to obtain a range of MKs to further explore their pharmacological activities, structure-activity relationships, and applications, a chemical screening method for MK-producing strains was established based on high-performance liquid chromatography-ultraviolet (HPLC-UV) technology. Considering that Bacillus strains have proven to be an important MK-producing bioresource, twenty-nine putative Bacillus isolates previously sought from a fermented soybean sample were used for the validation of the chemical screening method, which ultimately led to the discovery of sixteen MK-producing strains. Among them, Bacillus subtilis DC-1 presented excellent ability to produce MKs. Another, a purchased strain of B. amyloliquefaciens was discovered to be an MK-producing strain. These results indicated this screening method was simple and highly efficient for the discovery of MK-producing strains, especially those producing a range of MK structures.

The flavonoid degrading fungus Acremonium sp. DSM 24697 produces two diglycosidases with different specificities

AbstractDiglycosidases hydrolyze the heterosidic linkage of diglycoconjugates, releasing the disaccharide and the aglycone. Usually, these enzymes do not hydrolyze or present only low activities towards monoglycosylated compounds. The flavonoid degrading fungus Acremonium sp. DSM 24697 produced two diglycosidases, which were termed 6-O-α-rhamnosyl-β-glucosidase I and II (αRβG I and II) because of their function of releasing the disaccharide rutinose (6-O-α-L-rhamnosyl-β-D-glucose) from the diglycoconjugates hesperidin or rutin. In this work, the genome of Acremonium sp. DSM 24697 was sequenced and assembled with a size of ~ 27 Mb. The genes encoding αRβG I and II were expressed in Pichia pastoris KM71 and the protein products were purified with apparent molecular masses of 42 and 82 kDa, respectively. A phylogenetic analysis showed that αRβG I grouped in glycoside hydrolase family 5, subfamily 23 (GH5), together with other fungal diglycosidases whose substrate specificities had been reported to be different from αRβG I. On the other hand, αRβG II grouped in glycoside hydrolase family 3 (GH3) and thus is the first GH3 member that hydrolyzes the heterosidic linkage of rutinosylated compounds. The substrate scopes of the enzymes were different: αRβG I showed exclusive specificity toward 7-O-β-rutinosyl flavonoids, whereas αRβG II hydrolyzed both 7-O-β-rutinosyl- and 3-O-β-rutinosyl- flavonoids. None of the enzymes displayed activity toward 7-O-β-neohesperidosyl- flavonoids. The recombinant enzymes also exhibited transglycosylation activities, transferring rutinose from hesperidin or rutin onto various alcoholic acceptors. The different substrate scopes of αRβG I and II may be part of an optimized strategy of the original microorganism to utilize different carbon sources.