Discovery of Mycothiogranaticins from Streptomyces vietnamensis GIMV4.0001 and the Regulatory Effect of Mycothiol on the Granaticin Biosynthesis

Abstract

Granaticins are benzoisochromanequinone polyketides with remarkable antibacterial and anticancer activities. Three sulfur-containing granaticin congeners, mycothiogranaticins A (1), B (2) and granaticin MA (3) were discovered from a granaticin-producing strain of Streptomyces vietnamensis GIMV4.0001. Two of them were structurally determined with mycothiol or N-acetylcysteine moieties and found to be bio-actively reluctant. Disruption of the mshA gene (SVTN_RS20640) that encodes the D-inositol-3-phosphate glycosyltransferase crucial for mycothiol biosynthesis, fully abolished the production of mycothiogranaticins. The result substantiated that the newly discovered mycothiogranaticins are consequences of the combination of the granaticin and mycothiol biosynthetic pathways. The overall granaticin production of the ΔmshA mutant strain was unexpectedly decreased by at least more than 50%, while similar production level of granaticins to that of the wild type strain was observed in an mycothiol-S transferase gene (SVTN_RS22215) disruptant Δmst. These results indicated that the mycothiol deficiency was responsible for the decreased production of granaticins. Mycothiol may positively regulate the biosynthesis of granaticin possibly by maintaining the cellular redox balance. To the best of our knowledge, this is the first report that mycothiol can not only be a direct building block of polyketides but also play a regulatory role in the polyketide biosynthesis.

An in-cluster Sfp-type phosphopantetheinyl transferase instead of the holo-ACP synthase activates the granaticin biosynthesis under natural physiological conditions

“…The methods for sample preparation and analysis were similar to those of our previous works ( Deng et al, 2020 ; Deng et al, 2021 ), but analyses were conducted on different apparatuses. For fermentation cultures, 5% (w/v) resins (Amberlite ® XAD16, Shanghai Macklin Biochemical Co., Ltd., China) were added into the cultures at the end of fermentation.…”

MPACT: An Advanced Informatics Tool for Metabolomics and Data Visualization of Specialized Metabolites from Complex Microbial Samples

“…The presence of these shunt products is particularly compelling given their capacity to facilitate combinatorial diversification of pyranonaphthoquinones through Michael addition, as has been documented between SEK-34B (a condensation product of 37) and granaticin to generate SEKgranaticin, 40 and analogously in the production of glenthimine A. 41 Additionally, granaticin MT (13), a mercapturic acid detoxification product of granaticin, 42 was upregulated in REE treated cultures, though this effect was not statistically significant.…”

“…Two features consistent with new thiolated metabolites were prioritized for isolation and structure elucidation due to their chemical differences from known granaticins, resulting in the identification of granaticin C ( 14) and granaticin D (15). Granaticin D was recently described as mycothiogranaticin A, 42 and is referred to herein as granaticin D to maintain consistency with existing nomenclature of thiolated pyranonaphthoquinones. [43][44][45] Granaticin C is a new compound with an unusual non-acylated cysteine sidechain, a modification that has not been previously reported for any electrophilic secondary metabolites subject to thiol detoxification pathways.…”

“…40 The presence of a new the mycothiol derivative granaticin D (15) was expected in light of previous reports of granaticin MT which was hypothesized to be generated through thiolation of granaticin A as is the case in similar adducts of electrophilic antibiotics such as kalafungin and nanaomycin. [43][44][45] However, the presence of a free cysteine derivative 14 was surprising, since to our knowledge, there have been no reports of an unacylated thiol derivative of an electrophilic natural product, with the majority of known thiolated compounds being thiol-linked dimers, 45 or mycothiol, 44 mercapturic acid, 42 or ergothioneine derivatives. 43 However, it remains unclear if granaticin C (14) was produced de novo from free cysteine or as a degradation product of granaticin MT, although Streptomyces sp.…”

Brominated and Sulfur-Containing Angucyclines Derived from a Single Pathway: Identification of Nocardiopsistins D–F

“…A study on the angucycline urdamycin E indicated that the methanethiol residue was derived from methionine and was incorporated as a whole via nonenzymatic conjugate addition . This suggested that nocardiopsistin E ( 2 ) might be generated via a similar nonenzymatic mechanism, and N-acetylcysteine thiol may also undergo a nonenzymatic conjugate addition to form nocardiopsistin F ( 3 ), like grixazone; alternatively, 3 might be generated via nonenzymatic incorporation using mycothiol (MSH) as the donor like naphthomycins J and granaticin MA. , …”