Total Synthesis of Kalimantacin A Davies, Jonathan A; Bull, Freya M; Walker, Paul D ...
Organic letters,
08/2020, Letnik:
22, Številka:
16
Journal Article
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Odprti dostop
The kalimantacins make up a family of hybrid polyketide-nonribosomal peptide-derived natural products that display potent and selective antibiotic activity against multidrug resistant strains of ...Staphylococcus aureus. Herein, we report the first total synthesis of kalimantacin A, in which three fragments are prepared and then united via Sonogashira and amide couplings. The enantioselective synthetic approach is convergent, unlocking routes to further kalimantacins and analogues for structure–activity relationship studies and clinical evaluation.
The enoyl‐acyl carrier protein reductase enzyme FabI is essential for fatty acid biosynthesis in Staphylococcus aureus and represents a promising target for the development of novel, urgently needed ...anti‐staphylococcal agents. Here, we elucidate the mode of action of the kalimantacin antibiotics, a novel class of FabI inhibitors with clinically‐relevant activity against multidrug‐resistant S. aureus. By combining X‐ray crystallography with molecular dynamics simulations, in vitro kinetic studies and chemical derivatization experiments, we characterize the interaction between the antibiotics and their target, and we demonstrate that the kalimantacins bind in a unique conformation that differs significantly from the binding mode of other known FabI inhibitors. We also investigate mechanisms of acquired resistance in S. aureus and identify key residues in FabI that stabilize the binding of the antibiotics. Our findings provide intriguing insights into the mode of action of a novel class of FabI inhibitors that will inspire future anti‐staphylococcal drug development.
Combating MRSA: The kalimantacin antibiotics mimic the conformation of the natural fatty acyl substrate to inhibit the activity of the essential enoyl‐ACP reductase enzyme FabI in Staphylococcus aureus. The findings of this study provide insights into the mode of action of this novel class of FabI inhibitors.
Bacterial trans‐acyltransferase polyketide synthases (trans‐AT PKSs) are modular megaenzymes that employ unusual catalytic domains to assemble diverse bioactive natural products. One such PKS is ...responsible for the biosynthesis of the oximidine anticancer agents, oxime‐substituted benzolactone enamides that inhibit vacuolar H+‐ATPases. Here, we describe the identification of the oximidine gene cluster in Pseudomonas baetica and the characterization of four novel oximidine variants, including a structurally simpler intermediate that retains potent anticancer activity. Using a combination of in vivo, in vitro and computational approaches, we experimentally elucidate the oximidine biosynthetic pathway and reveal an unprecedented mechanism for O‐methyloxime formation. We show that this process involves a specialized monooxygenase and methyltransferase domain and provide insight into their activity, mechanism and specificity. Our findings expand the catalytic capabilities of trans‐AT PKSs and identify potential strategies for the production of novel oximidine analogues.
The anticancer agent oximidine I and three novel variants were discovered as products of a cryptic trans‐AT PKS/NRPS in Pseudomonas baetica. By manipulating the biosynthetic pathway, a key intermediate was identified that retains potent anticancer properties. A combination of bioinformatics analysis and genetic and biochemical experiments illuminated the oximidine biosynthetic pathway, including a novel mechanism for O‐methyloxime formation.
Mupirocin is a clinically important antibiotic produced by Pseudomonas fluorescens NCIMB 10586 that is assembled by a complex trans‐AT polyketide synthase. The polyketide fragment, monic acid, is ...esterified by a 9‐hydroxynonanoic acid (9HN) side chain which is essential for biological activity. The ester side chain assembly is initialised from a 3‐hydroxypropionate (3HP) starter unit attached to the acyl carrier protein (ACP) MacpD, but the fate of this species is unknown. Herein we report the application of NMR spectroscopy, mass spectrometry, chemical probes and in vitro assays to establish the remaining steps of 9HN biosynthesis. These investigations reveal a complex interplay between a novel iterative or “stuttering” KS‐AT didomain (MmpF), the multidomain module MmpB and multiple ACPs. This work has important implications for understanding the late‐stage biosynthetic steps of mupirocin and will be important for future engineering of related trans‐AT biosynthetic pathways (e.g. thiomarinol).
Mupirocin is a clinically important antibiotic in which the polyketide fragment, monic acid, is esterified to a 9‐hydroxynonanoic acid (9HN) side chain, which is essential for biological activity. NMR spectroscopy, mass spectrometry, chemical probes and in vitro assays were used to establish how 9HN is assembled through the action of multiple acyl carrier proteins, two ketosynthases and fatty acid β‐keto processing enzymes.
Mupirocin, a commercially available antibiotic produced by Pseudomonas fluorescens NCIMB 10586, and thiomarinol, isolated from the marine bacterium Pseudoalteromonas sp. SANK 73390, both consist of a ...polyketide-derived monic acid homologue esterified with either 9-hydroxynonanoic acid (mupirocin, 9HN) or 8-hydroxyoctanoic acid (thiomarinol, 8HO). The mechanisms of formation of these deceptively simple 9HN and 8HO fatty acid moieties in mup and tml, respectively, remain unresolved. To define starter unit generation, the purified mupirocin proteins MupQ, MupS, and MacpD and their thiomarinol equivalents (TmlQ, TmlS and TacpD) have been expressed and shown to convert malonyl coenzyme A (CoA) and succinyl CoA to 3-hydroxypropionoyl (3-HP) or 4-hydroxybutyryl (4-HB) fatty acid starter units, respectively, via the MupQ/TmlQ catalyzed generation of an unusual bis-CoA/acyl carrier protein (ACP) thioester, followed by MupS/TmlS catalyzed reduction. Mix and match experiments show MupQ/TmlQ to be highly selective for the correct CoA. MacpD/TacpD were interchangeable but alternate trans-acting ACPs from the mupirocin pathway (MacpA/TacpA) or a heterologous ACP (BatA) were nonfunctional. MupS and TmlS selectivity was more varied, and these reductases differed in their substrate and ACP selectivity. The solution structure of MacpD determined by NMR revealed a C-terminal extension with partial helical character that has been shown to be important for maintaining high titers of mupirocin. We generated a truncated MacpD construct, MacpD_T, which lacks this C-terminal extension but retains an ability to generate 3-HP with MupS and MupQ, suggesting further downstream roles in protein–protein interactions for this region of the ACP.
The presence of β‐branches in the structure of polyketides that possess potent biological activity underpins the widespread importance of this structural feature. Kalimantacin is a polyketide ...antibiotic with selective activity against staphylococci, and its biosynthesis involves the unprecedented incorporation of three different and sequential β‐branching modifications. We use purified single and multi‐domain enzyme components of the kalimantacin biosynthetic machinery to address in vitro how the pattern of β‐branching in kalimantacin is controlled. Robust discrimination of enzyme products required the development of a generalisable assay that takes advantage of 13C NMR of a single 13C label incorporated into key biosynthetic mimics combined with favourable dynamic properties of an acyl carrier protein. We report a previously unassigned modular enoyl‐CoA hydratase (mECH) domain and the assembly of enzyme constructs and cascades that are able to generate each specific β‐branch.
Branching out: A direct 13C NMR assay was applied to monitor model biosynthetic intermediates bound to an acyl carrier protein (ACP). This assay was used in conjunction with multienzyme cascades to show how the pattern of β‐branching in the polyketide antibiotic kalimantacin is controlled.
The presence of β-branches in the structure of polyketides that possess potent biological activity underpins the widespread importance of this structural feature. Kalimantacin is a polyketide ...antibiotic with selective activity against staphylococci, and its biosynthesis involves the unprecedented incorporation of three different and sequential β-branching modifications. We use purified single and multi-domain enzyme components of the kalimantacin biosynthetic machinery to address in vitro how the pattern of β-branching in kalimantacin is controlled. Robust discrimination of enzyme products required the development of a generalisable assay that takes advantage of
C NMR of a single
C label incorporated into key biosynthetic mimics combined with favourable dynamic properties of an acyl carrier protein. We report a previously unassigned modular enoyl-CoA hydratase (mECH) domain and the assembly of enzyme constructs and cascades that are able to generate each specific β-branch.
Bacterial trans‐acyltransferase polyketide synthases (trans‐AT PKSs) are modular megaenzymes that employ unusual catalytic domains to assemble diverse bioactive natural products. One such PKS is ...responsible for the biosynthesis of the oximidine anticancer agents, oxime‐substituted benzolactone enamides that inhibit vacuolar H+‐ATPases. Here, we describe the identification of the oximidine gene cluster in Pseudomonas baetica and the characterization of four novel oximidine variants, including a structurally simpler intermediate that retains potent anticancer activity. Using a combination of in vivo, in vitro and computational approaches, we experimentally elucidate the oximidine biosynthetic pathway and reveal an unprecedented mechanism for O‐methyloxime formation. We show that this process involves a specialized monooxygenase and methyltransferase domain and provide insight into their activity, mechanism and specificity. Our findings expand the catalytic capabilities of trans‐AT PKSs and identify potential strategies for the production of novel oximidine analogues.
The anticancer agent oximidine I and three novel variants were discovered as products of a cryptic trans‐AT PKS/NRPS in Pseudomonas baetica. By manipulating the biosynthetic pathway, a key intermediate was identified that retains potent anticancer properties. A combination of bioinformatics analysis and genetic and biochemical experiments illuminated the oximidine biosynthetic pathway, including a novel mechanism for O‐methyloxime formation.
Mupirocin is a clinically important antibiotic produced by Pseudomonas fluorescens NCIMB 10586 that is assembled by a complex trans‐AT polyketide synthase. The polyketide fragment, monic acid, is ...esterified by a 9‐hydroxynonanoic acid (9HN) side chain which is essential for biological activity. The ester side chain assembly is initialised from a 3‐hydroxypropionate (3HP) starter unit attached to the acyl carrier protein (ACP) MacpD, but the fate of this species is unknown. Herein we report the application of NMR spectroscopy, mass spectrometry, chemical probes and in vitro assays to establish the remaining steps of 9HN biosynthesis. These investigations reveal a complex interplay between a novel iterative or “stuttering” KS‐AT didomain (MmpF), the multidomain module MmpB and multiple ACPs. This work has important implications for understanding the late‐stage biosynthetic steps of mupirocin and will be important for future engineering of related trans‐AT biosynthetic pathways (e.g. thiomarinol).
Mupirocin is a clinically important antibiotic in which the polyketide fragment, monic acid, is esterified to a 9‐hydroxynonanoic acid (9HN) side chain, which is essential for biological activity. NMR spectroscopy, mass spectrometry, chemical probes and in vitro assays were used to establish how 9HN is assembled through the action of multiple acyl carrier proteins, two ketosynthases and fatty acid β‐keto processing enzymes.
The enoyl‐acyl carrier protein reductase enzyme FabI is essential for fatty acid biosynthesis in Staphylococcus aureus and represents a promising target for the development of novel, urgently needed ...anti‐staphylococcal agents. Here, we elucidate the mode of action of the kalimantacin antibiotics, a novel class of FabI inhibitors with clinically‐relevant activity against multidrug‐resistant S. aureus. By combining X‐ray crystallography with molecular dynamics simulations, in vitro kinetic studies and chemical derivatization experiments, we characterize the interaction between the antibiotics and their target, and we demonstrate that the kalimantacins bind in a unique conformation that differs significantly from the binding mode of other known FabI inhibitors. We also investigate mechanisms of acquired resistance in S. aureus and identify key residues in FabI that stabilize the binding of the antibiotics. Our findings provide intriguing insights into the mode of action of a novel class of FabI inhibitors that will inspire future anti‐staphylococcal drug development.
Combating MRSA: The kalimantacin antibiotics mimic the conformation of the natural fatty acyl substrate to inhibit the activity of the essential enoyl‐ACP reductase enzyme FabI in Staphylococcus aureus. The findings of this study provide insights into the mode of action of this novel class of FabI inhibitors.
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