Acarbose is a bacterial-derived α-glucosidase inhibitor clinically used to treat patients with type 2 diabetes. As type 2 diabetes is on the rise worldwide, the market demand for acarbose has also ...increased. Despite its significant therapeutic importance, how it is made in nature is not completely understood. Here, we report the complete biosynthetic pathway to acarbose and its structural components, GDP-valienol and O-4-amino-(4,6-dideoxy-α-D-glucopyranosyl)-(1→4)-O-α-D-glucopyranosyl-(1→4)-D-glucopyranose. GDP-valienol is derived from valienol 7-phosphate, catalyzed by three cyclitol modifying enzymes, whereas O-4-amino-(4,6-dideoxy-α-D-glucopyranosyl)-(1→4)-O-α-D-glucopyranosyl-(1→4)-D-glucopyranose is produced from dTDP-4-amino-4,6-dideoxy-D-glucose and maltose by the glycosyltransferase AcbI. The final assembly process is catalyzed by a pseudoglycosyltransferase enzyme, AcbS, which is a homologue of AcbI but catalyzes the formation of a non-glycosidic C-N bond. This study clarifies all previously unknown steps in acarbose biosynthesis and establishes a complete pathway to this high value pharmaceutical.
Acarbose is a well-known microbial specialized metabolite used clinically to treat type 2 diabetes. This natural pseudo-oligosaccharide (PsOS) shows potent inhibitory activity toward various glycosyl ...hydrolases, including α-glucosidases and α-amylases. While acarbose and other PsOSs are produced by many different bacteria, their ecological or biological role in microbial communities is still an open question. Here, we show that several PsOS-producing actinobacteria, i.e., Actinoplanes sp. SE50/110 (acarbose producer), Streptomyces glaucescens GLA.O (acarbose producer), and Streptomyces dimorphogenes ATCC 31484 (trestatin producer), can grow in the presence of acarbose, while the growth of the non-PsOS-producing organism Streptomyces coelicolor M1152 was suppressed when starch is the main source of energy. Further investigations using recombinant α-amylases from S. coelicolor M1152 and the PsOS-producing actinobacteria revealed that the S. coelicolor α-amylase was inhibited by acarbose, whereas those from the PsOS-producing bacteria were not inhibited by acarbose. Bioinformatic and protein modeling studies suggested that a point mutation in the α-amylases of the PsOS-producing actinobacteria is responsible for the resistance of those enzymes toward acarbose. Converting the acarbose-resistant α-amylase AcbE to its A304H variant diminished its acarbose-resistance property. Taken together, the results suggest that acarbose is used by the producing bacteria as a competitive exclusion agent to suppress the growth of other microorganisms in their natural environment, while the producing organisms equip themselves with α-amylase variants that are resistant to acarbose.
This review covers microbial secondary metabolites classified in the family of C7N aminocyclitols, a relatively new class of natural products that is increasingly gaining recognition due to their ...significant biomedical and agricultural uses. Their discovery and structure determinations, their biosynthetic origin, biological properties, chemical synthesis, as well as their further development for pharmaceutical uses are described. The literature from 1970 to July 2002 is reviewed, with 269 references cited.
Sesbagrandiflorains A (1) and B (2), isolated from the stem bark of the Indonesian fabaceous plant
Sesbania grandiflora
, were reported to be ...6-methoxy-2-(2´,3´-dihydroxy-5´-methoxyphenyl)-1-benzofuran-3-carbaldehyde and 6-hydroxy-2-(2´,3´-dihydroxy-5´-methoxyphenyl)-1-benzofuran-3-carbaldehyde, respectively. However, based on reevaluation of their 1D and 2D NMR data, the chemical structures of 1 and 2 have been revised to 4-hydroxy-2-(4´-hydroxy-2´-methoxyphenyl)-6-methoxybenzofuran-3-carbaldehyde and 4-hydroxy-2-(4´-hydroxy-2´-hydroxyphenyl)-6-methoxybenzofuran-3-carbaldehyde, respectively. In addition, seven new derivatives of
1
have been synthesized from the natural product in good yields (65 − 93%). The chemical structures of the synthetic compounds—one diester (6), four ethers (7–10), one secondary amine (11), and one oxime (12)—were confirmed by MS and NMR analysis. Compound 6 exhibited moderate antibacterial activity against the plant pathogen
Rhodococcus fascians
with a MIC of 0.1 mg/mL. Compounds 8 and 12 demonstrated respectable cytotoxicity against A375 melanoma cancer cells line with the relative IC
50
values of 22.8 and 32.7 μM, respectively.
Ultraviolet-protective compounds, such as mycosporine-like amino acids (MAAs) and related gadusols produced by some bacteria, fungi, algae, and marine invertebrates, are critical for the survival of ...reef-building corals and other marine organisms exposed to high-solar irradiance. These compounds have also been found in marine fish, where their accumulation is thought to be of dietary or symbiont origin. In this study, we report the unexpected discovery that fish can synthesize gadusol de novo and that the analogous pathways are also present in amphibians, reptiles, and birds. Furthermore, we demonstrate that engineered yeast containing the fish genes can produce and secrete gadusol. The discovery of the gadusol pathway in vertebrates provides a platform for understanding its role in these animals, and the possibility of engineering yeast to efficiently produce a natural sunscreen and antioxidant presents an avenue for its large-scale production for possible use in pharmaceuticals and cosmetics.
Glycosylation is a common modification reaction in natural product biosynthesis and has been known to be a post-assembly line tailoring process in glycosylated polyketide biosynthesis. Here, we show ...that in pactamycin biosynthesis, glycosylation can take place on an acyl carrier protein (ACP)-bound polyketide intermediate. Using in vivo gene inactivation, chemical complementation and in vitro pathway reconstitution, we demonstrate that the 3-aminoacetophenone moiety of pactamycin is derived from 3-aminobenzoic acid by a set of discrete polyketide synthase proteins via a 3-(3-aminophenyl)3-oxopropionyl-ACP intermediate. This ACP-bound intermediate is then glycosylated by an N-glycosyltransferase, PtmJ, providing a sugar precursor for the formation of the aminocyclopentitol core structure of pactamycin. This is the first example of glycosylation of a small molecule while tethered to a carrier protein. Additionally, we demonstrate that PtmO is a hydrolase that is responsible for the release of the ACP-bound product to a free β-ketoacid that subsequently undergoes decarboxylation.
Pactamycin, a structurally unique aminocyclitol natural product isolated from
Streptomyces pactum
, has potent antibacterial, antitumor, and anti-protozoa activities. However, its production yields ...under currently used culture conditions are generally low. To understand how pactamycin biosynthesis is regulated and explore the possibility of improving pactamycin production in
S. pactum
, we investigated the transcription regulations of pactamycin biosynthesis. In vivo inactivation of two putative pathway-specific regulatory genes,
ptmE
and
ptmF
, resulted in mutant strains that are not able to produce pactamycin. Genetic complementation using a cassette containing
ptmE and ptmF
integrated into the
S. pactum
chromosome rescued the production of pactamycin. Transcriptional analysis of the Δ
ptmE
and Δ
ptmF
strains suggests that both genes control the expression of the whole pactamycin biosynthetic gene cluster. However, attempts to overexpress these regulatory genes by introducing a second copy of the genes in
S. pactum
did not improve the production yield of pactamycin. We discovered that pactamycin biosynthesis is sensitive to phosphate regulation. Concentration of inorganic phosphate higher than 2 mM abolished both the transcription of the biosynthetic genes and the production of the antibiotic. Draft genome sequencing of
S. pactum
and bioinformatics studies revealed the existence of global regulatory genes, e.g., genes that encode a two-component PhoR-PhoP system, which are commonly involved in secondary metabolism. Inactivation of
phoP
did not show any significant effect to pactamycin production. However, in the
phoP
::
aac(3)IV
mutant, pactamycin biosynthesis is not affected by external inorganic phosphate concentration.
This review covers the biosynthesis of aminocyclitol-aminoglycoside antibiotics and related compounds, particularly from the molecular genetic perspectives. 195 references are cited.
Pactamycin is a structurally unique aminocyclitol antibiotic with broad-spectrum cell growth inhibitory activity. To explore the bountiful activity of the aminocyclitol core of pactamycin, an ...efficient, modular, and asymmetric synthesis of aminocyclopentitols resembling the pactamycin pharmacophore has been developed employing a SmI2-mediated imino-pinacol coupling strategy. Two of the compounds exhibited antitumor activity against A375 melanoma cells.
Pulmonary fibrosis is a scarring disease of lung tissue, which seriously threatens human health. Treatment options are currently limited, and effective strategies are still lacking. In the present ...study, 25 compounds were isolated from the deep-sea fungus
Trichoderma
sp. MCCC 3A01244. Among them, two β-carboline alkaloids, trichocarbolines A (
1
) and C (
4
) are new compounds. The chemical structures of these compounds were elucidated based on their HRESIMS, 1D and 2D NMR spectra, optical rotation calculation, and comparisons with data reported in the literature. Trichocarboline B (+)- and (–)-enantiomers had previously been synthesized, and this is its first report as a natural product. Their anti-pulmonary fibrosis (PF) activity and cytotoxicity were investigated. Compounds
1
,
11
, and
13
strongly inhibited TGF-β1-induced total collagen accumulation and showed low cytotoxicity against the HFL1 cell line. Further studies revealed compound
1
inhibited extracellular matrix (ECM) deposition by downregulating the expression of protein fibronectin (FN), proliferating cell nuclear antigen (PCNA), and α-smooth muscle actin (α-SMA). Mechanistic study revealed that compound
1
decreased pulmonary fibrosis by inhibiting the TGF-β/Smad signaling pathway. As a newly identified β-carboline alkaloid, compound
1
may be used as a lead compound for developing more efficient anti-pulmonary fibrosis agents.
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