Characterization of rhodosaminyl transfer by the AknS/AknT glycosylation complex and its use in reconstituting the biosynthetic pathway of aclacinomycin A

Rethinking Biosynthesis of Aclacinomycin A

Aclacinomycin A (ACM-A) is an anthracycline antitumor agent widely used in clinical practice. The current industrial production of ACM-A relies primarily on chemical synthesis and microbial fermentation. However, chemical synthesis involves multiple reactions which give rise to high production costs and environmental pollution. Microbial fermentation is a sustainable strategy, yet the current fermentation yield is too low to satisfy market demand. Hence, strain improvement is highly desirable, and tremendous endeavors have been made to decipher biosynthesis pathways and modify key enzymes. In this review, we comprehensively describe the reported biosynthesis pathways, key enzymes, and, especially, catalytic mechanisms. In addition, we come up with strategies to uncover unknown enzymes and improve the activities of rate-limiting enzymes. Overall, this review aims to provide valuable insights for complete biosynthesis of ACM-A.

Anthracyclines: biosynthesis, engineering and clinical applications

Covering: January 1995 to June 2021Anthracyclines are glycosylated microbial natural products that harbour potent antiproliferative activities. Doxorubicin has been widely used as an anticancer agent in the clinic for several decades, but its use is restricted due to severe side-effects such as cardiotoxicity. Recent studies into the mode-of-action of anthracyclines have revealed that effective cardiotoxicity-free anthracyclines can be generated by focusing on histone eviction activity, instead of canonical topoisomerase II poisoning leading to double strand breaks in DNA. These developments have coincided with an increased understanding of the biosynthesis of anthracyclines, which has allowed generation of novel compound libraries by metabolic engineering and combinatorial biosynthesis. Coupled to the continued discovery of new congeners from rare Actinobacteria, a better understanding of the biology of Streptomyces and improved production methodologies, the stage is set for the development of novel anthracyclines that can finally surpass doxorubicin at the forefront of cancer chemotherapy.

Directed Biosynthesis of Iso-aclacinomycins with Improved Anticancer Activity

A four-enzyme catalyzed hydroxy regioisomerization of anthracycline was integrated into the biosynthetic pathway of aclacinomycin A (ALM-A), to generate a series of iso-ALMs via directed combinatorial biosynthesis combined with precursor-directed mutasynthesis. Most of the newly acquired iso-ALMs exhibit obviously (1-5-fold) improved antitumor activity. Therefore, we not only developed iso-ALMs with potential as clinical drugs but also demonstrated the utility of this tailoring tool for modification of anthracycline antibiotics in drug discovery and development.

Enzymatic Synthesis of the C-Glycosidic Moiety of Nogalamycin R

Carbohydrate moieties are essential for the biological activity of anthracycline anticancer agents such as nogalamycin, which contains l-nogalose and l-nogalamine units. The former of these is attached through a canonical O-glycosidic linkage, but the latter is connected via an unusual dual linkage composed of C-C and O-glycosidic bonds. In this work, we have utilized enzyme immobilization techniques and synthesized l-rhodosamine-thymidine diphosphate (TDP) from α-d-glucose-1-TDP using seven enzymes. In a second step, we assembled the dual linkage system by attaching the aminosugar to an anthracycline aglycone acceptor using the glycosyl transferase SnogD and the α-ketoglutarate dependent oxygenase SnoK. Furthermore, our work indicates that the auxiliary P450-type protein SnogN facilitating glycosylation is surprisingly associated with attachment of the neutral sugar l-nogalose rather than the aminosugar l-nogalamine in nogalamycin biosynthesis.

Coculture of Marine Invertebrate-Associated Bacteria and Interdisciplinary Technologies Enable Biosynthesis and Discovery of a New Antibiotic, Keyicin

Advances in genomics and metabolomics have made clear in recent years that microbial biosynthetic capacities on Earth far exceed previous expectations. This is attributable, in part, to the realization that most microbial natural product (NP) producers harbor biosynthetic machineries not readily amenable to classical laboratory fermentation conditions. Such "cryptic" or dormant biosynthetic gene clusters (BGCs) encode for a vast assortment of potentially new antibiotics and, as such, have become extremely attractive targets for activation under controlled laboratory conditions. We report here that coculturing of a Rhodococcus sp. and a Micromonospora sp. affords keyicin, a new and otherwise unattainable bis-nitroglycosylated anthracycline whose mechanism of action (MOA) appears to deviate from those of other anthracyclines. The structure of keyicin was elucidated using high resolution MS and NMR technologies, as well as detailed molecular modeling studies. Sequencing of the keyicin BGC (within the Micromonospora genome) enabled both structural and genomic comparisons to other anthracycline-producing systems informing efforts to characterize keyicin. The new NP was found to be selectively active against Gram-positive bacteria including both Rhodococcus sp. and Mycobacterium sp. E. coli-based chemical genomics studies revealed that keyicin's MOA, in contrast to many other anthracyclines, does not invoke nucleic acid damage.

Two Cooperative Glycosyltransferases Are Responsible for the Sugar Diversity of Saquayamycins Isolated from Streptomyces sp. KY 40-1

Glycosyltransferases are key enzymes involved in the biosynthesis of valuable natural products providing an excellent drug-tailoring tool. Herein, we report the identification of two cooperative glycosyltransferases from the sqn gene cluster directing the biosynthesis of saquayamycins in Streptomyces sp. KY40-1: SqnG1 and SqnG2. Gene inactivation of sqnG1 leads to 50-fold decrease in saquayamycin production, while inactivation of sqnG2 leads to complete production loss, suggesting that SqnG2 acts as dual O- and C-glycosyltransferase. Gene inactivation of a third putative glycosyltransferase-encoding gene, sqnG3, does not affect saquayamycin production in a major way, suggesting that SqnG3 has no or a supportive role in glycosylation. The data indicate that SqnG1 and SqnG2 are solely and possibly cooperatively responsible for the sugar diversity observed in saquayamycins 1-7. This is the first evidence of a glycosyltransferase system showing codependence to achieve dual O- and C-glycosyltransferase activity, utilizing NDP-activated d-olivose, l-rhodinose, as well as an unusual amino sugar, presumably 3,6-dideoxy-l-idosamine.

Elucidating the Sugar Tailoring Steps in the Cytorhodin Biosynthetic Pathway

Anthracycline antitumor cytorhodins X and Y feature a rare 9α-glycoside and 7-dexoy-aglycone. Characterization of the cytorhodin gene cluster from Streptomyces sp. SCSIO 1666 through gene inactivations and metabolite analyses reveals three glycosyltransferases (GTs) involved in the sugar tailoring steps. The duo of CytG1 and CytL effects C-7 glycosylation with l-rhodosamine whereas the iterative GT CytG3 and CytW similarly modifies both C-9 and C-10 positions. CytG2 also acts iteratively by incorporating the second and third sugar moiety into the trisaccharide chains at the C-7 or C-10 position.

One-Pot Combinatorial Biosynthesis of Glycosylated Anthracyclines by Cocultivation of Streptomyces Strains Producing Aglycones and Nucleotide Deoxysugars

Anthracyclines, such as doxorubicin, are effective anticancer drugs composed of a tetracyclic polyketide aglycone and one or more deoxysugar moieties, which play a critical role in their biological activity. A facile one-pot combinatorial biosynthetic system was developed for the generation of a range of glycosylated derivatives of anthracyclines. Cocultivation of Streptomyces venezuelae mutants producing two anthracycline aglycones with eight different nucleotide deoxysugar-producing S. venezuelae mutants that coexpress a substrate-flexible glycosyltransferase led to the generation of 16 aklavinone or ε-rhodomycinone glycosides containing diverse deoxysugar moieties, seven of which are new. This demonstrates the potential of the one-pot combinatorial biosynthetic system based on cocultivation as a facile biological tool capable of combining diverse aglycones and deoxysugars to generate structurally diverse polyketides carrying engineered sugars for drug discovery and development.

New insights into paulomycin biosynthesis pathway in Streptomyces albus J1074 and generation of novel derivatives by combinatorial biosynthesis

Background

Streptomyces albus J1074 produces glycosylated antibiotics paulomycin A, B and E that derive from chorismate and contain an isothiocyanate residue in form of paulic acid. Paulomycins biosynthesis pathway involves two glycosyltransferases, three acyltransferases, enzymes required for paulic acid biosynthesis (in particular an aminotransferase and a sulfotransferase), and enzymes involved in the biosynthesis of two deoxysugar moieties: D-allose and L-paulomycose.

Results

Inactivation of genes encoding enzymes involved in deoxysugar biosynthesis, paulic acid biosynthesis, deoxysugar transfer, and acyl moieties transfer has allowed the identification of several biosynthetic intermediates and shunt products, derived from paulomycin intermediates, and to propose a refined version of the paulomycin biosynthesis pathway. Furthermore, several novel bioactive derivatives of paulomycins carrying modifications in the L-paulomycose moiety have been generated by combinatorial biosynthesis using different plasmids that direct the biosynthesis of alternative deoxyhexoses.

Conclusions

The paulomycins biosynthesis pathway has been defined by inactivation of genes encoding glycosyltransferases, acyltransferases and enzymes involved in paulic acid and L-paulomycose biosynthesis. These experiments have allowed the assignment of each of these genes to specific paulomycin biosynthesis steps based on characterization of products accumulated by the corresponding mutant strains. In addition, novel derivatives of paulomycin A and B containing L-paulomycose modified moieties were generated by combinatorial biosynthesis. The production of such derivatives shows that L-paulomycosyl glycosyltransferase Plm12 possesses a certain degree of flexibility for the transfer of different deoxysugars. In addition, the pyruvate dehydrogenase system form by Plm8 and Plm9 is also flexible to catalyze the attachment of a two-carbon side chain, derived from pyruvate, into both 2,6-dideoxyhexoses and 2,3,6-trideoxyhexoses. The activity of the novel paulomycin derivatives carrying modifications in the L-paulomycose moiety is lower than the original compounds pointing to some interesting structure–activity relationships.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0452-4) contains supplementary material, which is available to authorized users.

Glycosyltransferases: mechanisms and applications in natural product development

Glycosylation reactions mainly catalyzed by glycosyltransferases (Gts) occur almost everywhere in the biosphere, and always play crucial roles in vital processes.

Unconventional origin and hybrid system for construction of pyrrolopyrrole moiety in kosinostatin biosynthesis

Kosinostatin (KST), an antitumor antibiotic, features a pyrrolopyrrole moiety spirally jointed to a five-membered ring of an anthraquinone framework glycosylated with a γ-branched octose. By a combination of in silico analysis, genetic characterization, biochemical assay, and precursor feeding experiments, a biosynthetic pathway for KST was proposed, which revealed (1) the pyrrolopyrrole moiety originates from nicotinic acid and ribose, (2) the bicyclic amidine is constructed by a process similar to the tryptophan biosynthetic pathway, and (3) a discrete adenylation enzyme and a peptidyl carrier protein (PCP) are responsible for producing a PCP-tethered building block parallel to type II polyketide synthase (PKS) rather than for the PKS priming step by providing the starter unit. These findings provide an opportunity to further explore the inexplicable enzymatic logic that governs the formation of pyrrolopyrrole moiety and the spirocyclic skeleton.

Development of a Streptomyces venezuelae-based combinatorial biosynthetic system for the production of glycosylated derivatives of doxorubicin and its biosynthetic intermediates

Doxorubicin, one of the most widely used anticancer drugs, is composed of a tetracyclic polyketide aglycone and l-daunosamine as a deoxysugar moiety, which acts as an important determinant of its biological activity. This is exemplified by the fewer side effects of semisynthetic epirubicin (4'-epi-doxorubicin). An efficient combinatorial biosynthetic system that can convert the exogenous aglycone ε-rhodomycinone into diverse glycosylated derivatives of doxorubicin or its biosynthetic intermediates, rhodomycin D and daunorubicin, was developed through the use of Streptomyces venezuelae mutants carrying plasmids that direct the biosynthesis of different nucleotide deoxysugars and their transfer onto aglycone, as well as the postglycosylation modifications. This system improved epirubicin production from ε-rhodomycinone by selecting a substrate flexible glycosyltransferase, AknS, which was able to transfer the unnatural sugar donors and a TDP-4-ketohexose reductase, AvrE, which efficiently supported the biosynthesis of TDP-4-epi-l-daunosamine. Furthermore, a range of doxorubicin analogs containing diverse deoxysugar moieties, seven of which are novel rhodomycin D derivatives, were generated. This provides new insights into the functions of deoxysugar biosynthetic enzymes and demonstrates the potential of the S. venezuelae-based combinatorial biosynthetic system as a simple biological tool for modifying structurally complex sugar moieties attached to anthracyclines as an alternative to chemical syntheses for improving anticancer agents.

Enhancement of doxorubicin production by expression of structural sugar biosynthesis and glycosyltransferase genes in Streptomyces peucetius

To enhance doxorubicin (DXR) production, the structural sugar biosynthesis genes desIII and desIV from Streptomyces venezuelae ATCC 15439 and the glycosyltransferase pair dnrS/dnrQ from Streptomyces peucetius ATCC 27952 were cloned into the expression vector pIBR25, which contains a strong ermE promoter. The recombinant plasmids pDnrS25 and pDnrQS25 were constructed for overexpression of dnrS and the dnrS/dnrQ pair, whereas pDesSD25 and pDesQS25 were constructed to express desIII/desIV and dnrS/dnrQ-desIII/desIV, respectively. All of these recombinant plasmids were introduced into S. peucetius ATCC 27952. The recombinant strains produced more DXR than the S. peucetius parental strain: a 1.2-fold increase with pDnrS25, a 2.8-fold increase with pDnrQS25, a 2.6-fold increase with pDesSD25, and a 5.6-fold increase with pDesQS25. This study showed that DXR production was significantly enhanced by overexpression of potential biosynthetic sugar genes and glycosyltransferase.

Natural-product sugar biosynthesis and enzymatic glycodiversification

Many biologically active small-molecule natural products produced by microorganisms derive their activities from sugar substituents. Changing the structures of these sugars can have a profound impact on the biological properties of the parent compounds. This realization has inspired attempts to derivatize the sugar moieties of these natural products through exploitation of the sugar biosynthetic machinery. This approach requires an understanding of the biosynthetic pathway of each target sugar and detailed mechanistic knowledge of the key enzymes. Scientists have begun to unravel the biosynthetic logic behind the assembly of many glycosylated natural products and have found that a core set of enzyme activities is mixed and matched to synthesize the diverse sugar structures observed in nature. Remarkably, many of these sugar biosynthetic enzymes and glycosyltransferases also exhibit relaxed substrate specificity. The promiscuity of these enzymes has prompted efforts to modify the sugar structures and alter the glycosylation patterns of natural products through metabolic pathway engineering and enzymatic glycodiversification. In applied biomedical research, these studies will enable the development of new glycosylation tools and generate novel glycoforms of secondary metabolites with useful biological activity.

Natural-product sugar biosynthesis and enzymatic glycodiversification

Many biologically active small-molecule natural products produced by microorganisms derive their activities from sugar substituents. Changing the structures of these sugars can have a profound impact on the biological properties of the parent compounds. This realization has inspired attempts to derivatize the sugar moieties of these natural products through exploitation of the sugar biosynthetic machinery. This approach requires an understanding of the biosynthetic pathway of each target sugar and detailed mechanistic knowledge of the key enzymes. Scientists have begun to unravel the biosynthetic logic behind the assembly of many glycosylated natural products and have found that a core set of enzyme activities is mixed and matched to synthesize the diverse sugar structures observed in nature. Remarkably, many of these sugar biosynthetic enzymes and glycosyltransferases also exhibit relaxed substrate specificity. The promiscuity of these enzymes has prompted efforts to modify the sugar structures and alter the glycosylation patterns of natural products through metabolic pathway engineering and enzymatic glycodiversification. In applied biomedical research, these studies will enable the development of new glycosylation tools and generate novel glycoforms of secondary metabolites with useful biological activity.