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Xie X, Garg A, Khosla C, Cane DE. Elucidation of the Cryptic Methyl Group Epimerase Activity of Dehydratase Domains from Modular Polyketide Synthases Using a Tandem Modules Epimerase Assay. J Am Chem Soc 2017; 139:9507-9510. [PMID: 28682630 DOI: 10.1021/jacs.7b05502] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dehydratase (DH) domains of cryptic function are often found in polyketide synthase (PKS) modules that produce epimerized (2S)-2-methyl-3-ketoacyl-ACP (acyl carrier protein) intermediates. A combination of tandem equilibrium isotope exchange (EIX) and a newly developed Tandem Modules Epimerase assay revealed the intrinsic epimerase activity of NanDH1 and NanDH5, from modules 1 and 5, respectively, of the nanchangmycin (1) PKS as well of NigDH1, from module 1 of the nigericin (3) PKS. Unexpectedly, all three epimerase-active DH domains were also found to possess intrinsic dehydratase activity, whereas the conventional DH domains, EryDH4, from module 4 of the erythromycin synthase, and NanDH2 from module 2 of the nanchangmycin synthase, were shown to have cryptic epimerase activity.
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Affiliation(s)
- Xinqiang Xie
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
| | - Ashish Garg
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
| | - Chaitan Khosla
- Departments of Chemical Engineering, Chemistry, and Biochemistry, Stanford University , Stanford, California 94305, United States
| | - David E Cane
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
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2
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Keatinge-Clay AT. Polyketidsynthase-Module: eine Neudefinition. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Adrian T. Keatinge-Clay
- Department of Molecular Biosciences; The University of Texas at Austin; 100 E. 24 St. Austin TX 78712 USA
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Abstract
The enzymology of 135 assembly lines containing primarily cis-acyltransferase modules is comprehensively analyzed, with greater attention paid to less common phenomena. Diverse online transformations, in which the substrate and/or product of the reaction is an acyl chain bound to an acyl carrier protein, are classified so that unusual reactions can be compared and underlying assembly-line logic can emerge. As a complement to the chemistry surrounding the loading, extension, and offloading of assembly lines that construct primarily polyketide products, structural aspects of the assembly-line machinery itself are considered. This review of assembly-line phenomena, covering the literature up to 2017, should thus be informative to the modular polyketide synthase novice and expert alike.
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Affiliation(s)
- Adrian T Keatinge-Clay
- Department of Molecular Biosciences, The University of Texas at Austin , Austin, Texas 78712, United States
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Keatinge-Clay AT. Polyketide Synthase Modules Redefined. Angew Chem Int Ed Engl 2017; 56:4658-4660. [PMID: 28322495 DOI: 10.1002/anie.201701281] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 02/24/2017] [Indexed: 11/06/2022]
Abstract
Modular redefinition: A long-standing paradigm in modular polyketide synthase enzymology, namely the definition of a module, has been challenged by Abe and co-workers in their recent study. With this new understanding has emerged renewed hope for engineering these assembly lines to produce new materials and medicines.
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Affiliation(s)
- Adrian T Keatinge-Clay
- Department of Molecular Biosciences, The University of Texas at Austin, 100 E. 24th St., Austin, TX, 78712, USA
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Xie X, Garg A, Khosla C, Cane DE. Mechanism and Stereochemistry of Polyketide Chain Elongation and Methyl Group Epimerization in Polyether Biosynthesis. J Am Chem Soc 2017; 139:3283-3292. [PMID: 28157306 DOI: 10.1021/jacs.7b00278] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The polyketide synthases responsible for the biosynthesis of the polyether antibiotics nanchangmycin (1) and salinomycin (4) harbor a number of redox-inactive ketoreductase (KR0) domains that are implicated in the generation of C2-epimerized (2S)-2-methyl-3-ketoacyl-ACP intermediates. Evidence that the natural substrate for the polyether KR0 domains is, as predicted, a (2R)-2-methyl-3-ketoacyl-ACP intermediate, came from a newly developed coupled ketosynthase (KS)-ketoreductase (KR) assay that established that the decarboxylative condensation of methylmalonyl-CoA with S-propionyl-N-acetylcysteamine catalyzed by the Nan[KS1][AT1] didomain from module 1 of the nanchangmycin synthase generates exclusively the corresponding (2R)-2-methyl-3-ketopentanoyl-ACP (7a) product. In tandem equilibrium isotope exchange experiments, incubation of [2-2H]-(2R,3S)-2-methyl-3-hydroxypentanoyl-ACP (6a) with redox-active, epimerase-inactive EryKR6 from module 6 of the 6-deoxyerythronolide B synthase and catalytic quantities of NADP+ in the presence of redox-inactive, recombinant NanKR10 or NanKR50, from modules 1 and 5 of the nanchangmycin synthase, or recombinant SalKR70 from module 7 of the salinomycin synthase, resulted in first-order, time-dependent washout of deuterium from 6a. Control experiments confirmed that this washout was due to KR0-catalyzed isotope exchange of the reversibly generated, transiently formed oxidation product [2-2H]-(2R)-2-methyl-3-ketopentanoyl-ACP (7a), consistent with the proposed epimerase activity of each of the KR0 domains. Although they belong to the superfamily of short chain dehydrogenase-reductases, the epimerase-active KR0 domains from polyether synthases lack one or both residues of the conserved Tyr-Ser dyad that has previously been implicated in KR-catalyzed epimerizations.
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Affiliation(s)
- Xinqiang Xie
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
| | - Ashish Garg
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
| | - Chaitan Khosla
- Departments of Chemical Engineering, Chemistry, and Biochemistry, Stanford University , Stanford, California 94305, United States
| | - David E Cane
- Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States
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Xie X, Garg A, Keatinge-Clay AT, Khosla C, Cane DE. Epimerase and Reductase Activities of Polyketide Synthase Ketoreductase Domains Utilize the Same Conserved Tyrosine and Serine Residues. Biochemistry 2016; 55:1179-86. [PMID: 26863427 DOI: 10.1021/acs.biochem.6b00024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The role of the conserved active site tyrosine and serine residues in epimerization catalyzed by polyketide synthase ketoreductase (PKS KR) domains has been investigated. Both mutant and wild-type forms of epimerase-active KR domains, including the intrinsically redox-inactive EryKR3° and PicKR3° as well as redox-inactive mutants of EryKR1, were incubated with [2-(2)H]-(2R,3S)-2-methyl-3-hydroxypentanoyl-SACP ([2-(2)H]-2) and 0.05 equiv of NADP(+) in the presence of the redox-active, epimerase-inactive EryKR6 domain. The residual epimerase activity of each mutant was determined by tandem equilibrium isotope exchange, in which the first-order, time-dependent washout of isotope from 2 was monitored by liquid chromatography-tandem mass spectrometry with quantitation of the deuterium content of the diagnostic pantetheinate ejection fragment (4). Replacement of the active site Tyr or Ser residues, alone or together, significantly reduced the observed epimerase activity of each KR domain with minimal effect on substrate binding. Our results demonstrate that the epimerase and reductase activities of PKS KR domains share a common active site, with both reactions utilizing the same pair of Tyr and Ser residues.
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Affiliation(s)
- Xinqiang Xie
- Department of Chemistry, Box H, Brown University , Providence, Rhode Island 02912-9108, United States
| | - Ashish Garg
- Department of Chemistry, Box H, Brown University , Providence, Rhode Island 02912-9108, United States
| | - Adrian T Keatinge-Clay
- Departments of Molecular Biosciences and Chemistry, The University of Texas at Austin , 1 University Station A5300, Austin, Texas 78712-0165, United States
| | - Chaitan Khosla
- Departments of Chemical Engineering, Chemistry, and Biochemistry, Stanford University , Stanford, California 94305, United States
| | - David E Cane
- Department of Chemistry, Box H, Brown University , Providence, Rhode Island 02912-9108, United States
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Gay D, You YO, Keatinge-Clay A, Cane DE. Structure and stereospecificity of the dehydratase domain from the terminal module of the rifamycin polyketide synthase. Biochemistry 2013; 52:8916-28. [PMID: 24274103 DOI: 10.1021/bi400988t] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
RifDH10, the dehydratase domain from the terminal module of the rifamycin polyketide synthase, catalyzes the stereospecific syn dehydration of the model substrate (2S,3S)-2-methyl-3-hydroxypentanoyl-RifACP10, resulting in the exclusive formation of (E)-2-methyl-2-pentenoyl-RifACP10. RifDH10 does not dehydrate any of the other three diastereomeric, RifACP10-bound, diketide thioester substrates. On the other hand, when EryACP6, from the sixth module of the erythromycin polyketide synthase, is substituted for RifACP10, RifDH10 stereospecifically dehydrates only (2R,3R)-2-methyl-3-hydroxypentanoyl-EryACP6 to give exclusively (E)-2-methyl-2-pentenoyl-EryACP6, with no detectable dehydration of any of the other three diastereomeric, EryACP6-bound, diketides. An identical alteration in substrate diastereospecificity was observed for the corresponding N-acetylcysteamine or pantetheine thioester analogues, regardless of acyl chain length or substitution pattern. Incubation of (2RS)-2-methyl-3-ketopentanoyl-RifACP10 with the didomain reductase-dehydratase RifKR10-RifDH10 yielded (E)-2-methyl-2-pentenoyl-RifACP10, the expected product of syn dehydration of (2S,3S)-2-methyl-3-hydroxypentanoyl-RifACP10, while incubation with the corresponding EryACP6-bound substrate, (2RS)-2-methyl-3-ketopentanoyl-EryACP6, gave only the reduction product (2S,3S)-2-methyl-3-hydroxypentanoyl-EryACP6 with no detectable dehydration. These results establish the intrinsic syn dehydration stereochemistry and substrate diastereoselectivity of RifDH10 and highlight the critical role of the natural RifACP10 domain in chaperoning the proper recognition and processing of the natural ACP-bound undecaketide substrate. The 1.82 Å resolution structure of RifDH10 reveals the atomic-resolution details of the active site and allows modeling of the syn dehydration of the (2S,3S)-2-methyl-3-hydroxyacyl-RifACP10 substrate. These results suggest that generation of the characteristic cis double bond of the rifamycins occurs after formation of the full-length RifACP10-bound acyclic trans-unsaturated undecaketide intermediate, most likely during the subsequent macrolactamization catalyzed by the amide synthase RifF.
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Affiliation(s)
- Darren Gay
- Department of Chemistry and Biochemistry, The University of Texas at Austin , 1 University Station A5300, Austin, Texas 78712-0165, United States
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Guo L, Wang D, Xu Y, Qiu B, Lin Z, Dai H, Yang HH, Chen G. Discrimination of enantiomers based on LSPR biosensors fabricated with weak enantioselective and nonselective receptors. Biosens Bioelectron 2013; 47:199-205. [DOI: 10.1016/j.bios.2013.03.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 03/03/2013] [Accepted: 03/04/2013] [Indexed: 12/11/2022]
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Porter JL, Tobias NJ, Pidot SJ, Falgner S, Tuck KL, Vettiger A, Hong H, Leadlay PF, Stinear TP. The cell wall-associated mycolactone polyketide synthases are necessary but not sufficient for mycolactone biosynthesis. PLoS One 2013; 8:e70520. [PMID: 23894666 PMCID: PMC3720922 DOI: 10.1371/journal.pone.0070520] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 06/26/2013] [Indexed: 11/23/2022] Open
Abstract
Mycolactones are polyketide-derived lipid virulence factors made by the slow-growing human pathogen, Mycobacterium ulcerans. Three unusually large and homologous plasmid-borne genes (mlsA1: 51 kb, mlsB: 42 kb and mlsA2: 7 kb) encode the mycolactone type I polyketide synthases (PKS). The extreme size and low sequence diversity of these genes has posed significant barriers for exploration of the genetic and biochemical basis of mycolactone synthesis. Here, we have developed a truncated, more tractable 3-module version of the 18-module mycolactone PKS and we show that this engineered PKS functions as expected in the natural host M. ulcerans to produce an additional polyketide; a triketide lactone (TKL). Cell fractionation experiments indicated that this 3-module PKS and the putative accessory enzymes encoded by mup045 and mup038 associated with the mycobacterial cell wall, a finding supported by confocal microscopy. We then assessed the capacity of the faster growing, Mycobacterium marinum to harbor and express the 3-module Mls PKS and accessory enzymes encoded by mup045 and mup038. RT-PCR, immunoblotting, and cell fractionation experiments confirmed that the truncated Mls PKS multienzymes were expressed and also partitioned with the cell wall material in M. marinum. However, this heterologous host failed to produce TKL. The systematic deconstruction of the mycolactone PKS presented here suggests that the Mls multienzymes are necessary but not sufficient for mycolactone synthesis and that synthesis is likely to occur (at least in part) within the mycobacterial cell wall. This research is also the first proof-of-principle demonstration of the potential of this enzyme complex to produce tailored small molecules through genetically engineered rearrangements of the Mls modules.
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Affiliation(s)
- Jessica L. Porter
- Department of Microbiology and Immunology, University of Melbourne, Victoria, Australia
| | - Nicholas J. Tobias
- Department of Microbiology and Immunology, University of Melbourne, Victoria, Australia
- Department of Microbiology, Monash University, Clayton, Victoria, Australia
| | - Sacha J. Pidot
- Department of Microbiology and Immunology, University of Melbourne, Victoria, Australia
| | - Steffen Falgner
- Department of Microbiology and Immunology, University of Melbourne, Victoria, Australia
| | - Kellie L. Tuck
- School of Chemistry, Monash University, Clayton, Victoria, Australia
| | - Andrea Vettiger
- Molecular Immunology Unit, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Hui Hong
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Peter F. Leadlay
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Timothy P. Stinear
- Department of Microbiology and Immunology, University of Melbourne, Victoria, Australia
- Department of Microbiology, Monash University, Clayton, Victoria, Australia
- * E-mail:
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10
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You YO, Khosla C, Cane DE. Stereochemistry of reductions catalyzed by methyl-epimerizing ketoreductase domains of polyketide synthases. J Am Chem Soc 2013; 135:7406-9. [PMID: 23659177 PMCID: PMC3699853 DOI: 10.1021/ja4014776] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ketoreductase (KR) domains from modular polyketide synthases (PKSs) catalyze the reduction of 2-methyl-3-ketoacyl acyl carrier protein (ACP) substrates and in certain cases epimerization of the 2-methyl group as well. The structural and mechanistic basis of epimerization is poorly understood, and only a small number of such KRs been studied. In this work, we studied three recombinant KR domains with putative epimerase activity: NysKR1 from module 1 of the nystatin PKS, whose stereospecificity can be predicted from both the protein sequence and the product structure; RifKR7 from module 7 of the rifamycin PKS, whose stereospecificity cannot be predicted from the protein sequence; and RifKR10 from module 10 of the rifamycin PKS, whose specificity is unclear from both the sequence and the structure. Each KR was individually incubated with NADPH and (2R)- or (2RS)-2-methyl-3-ketopentanoyl-ACP generated enzymatically in situ or via chemoenzymatic synthesis, respectively. Chiral GC-MS analysis revealed that each KR stereospecifically produced the corresponding (2S,3S)-2-methyl-3-hydroxypentanoyl-ACP in which the 2-methyl substituent had undergone KR-catalyzed epimerization. Thus, our results have led to the identification of a prototypical set of KR domains that generate (2S,3S)-2-methyl-3-hydroxyacyl products in the course of polyketide biosynthesis.
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Affiliation(s)
- Young-Ok You
- Department of Chemistry, Box H, Brown University, Providence, Rhode Island 02912-9108
| | - Chaitan Khosla
- Departments of Chemical Engineering, Chemistry, and Biochemistry, Stanford University, Stanford, California 94305
| | - David E. Cane
- Department of Chemistry, Box H, Brown University, Providence, Rhode Island 02912-9108
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Caffrey P. Dissecting complex polyketide biosynthesis. Comput Struct Biotechnol J 2012; 3:e201210010. [PMID: 24688670 PMCID: PMC3962154 DOI: 10.5936/csbj.201210010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 11/06/2012] [Accepted: 11/07/2012] [Indexed: 12/17/2022] Open
Abstract
Numerous bioactive natural products are synthesised by modular polyketide synthases. These compounds can be made in high yield by native multienzyme assembly lines. However, formation of analogues by genetically engineered systems is often considerably less efficient. Biochemical studies on intact polyketide synthase proteins have amassed a body of knowledge that is substantial but still incomplete. Recently, the constituent enzymes have been structurally characterised as discrete domains or didomains. These recombinant proteins have been used to reconstitute single extension cycles in vitro. This has given further insights into how the final stereochemistry of chiral centres in polyketides is determined. In addition, this approach has revealed how domains co-operate to ensure efficient transfer of growing intermediates along the assembly line. This work is leading towards more effective re-programming of these enzymes for use in synthesis of new medicinal compounds.
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Affiliation(s)
- Patrick Caffrey
- School of Biomolecular and Biomedical Science, Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
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Cracan V, Banerjee R. Novel B(12)-dependent acyl-CoA mutases and their biotechnological potential. Biochemistry 2012; 51:6039-46. [PMID: 22803641 DOI: 10.1021/bi300827v] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The recent spate of discoveries of novel acyl-CoA mutases has engendered a growing appreciation for the diversity of 5'-deoxyadenosylcobalamin-dependent rearrangement reactions. The prototype of the reaction catalyzed by these enzymes is the 1,2 interchange of a hydrogen atom with a thioester group leading to a change in the degree of carbon skeleton branching. These enzymes are predicted to share common architectural elements: a Rossman fold and a triose phosphate isomerase (TIM)-barrel domain for binding cofactor and substrate, respectively. Within this family, methylmalonyl-CoA mutase (MCM) is the best studied and is the only member found in organisms ranging from bacteria to man. MCM interconverts (2R)-methylmalonyl-CoA and succinyl-CoA. The more recently discovered family members include isobutyryl-CoA mutase (ICM), which interconverts isobutyryl-CoA and n-butyryl-CoA; ethylmalonyl-CoA mutase, which interconverts (2R)-ethylmalonyl-CoA and (2S)-methylsuccinyl-CoA; and 2-hydroxyisobutyryl-CoA mutase, which interconverts 2-hydroxyisobutyryl-CoA and (3S)-hydroxybutyryl-CoA. A variant in which the two subunits of ICM are fused to a G-protein chaperone, IcmF, has been described recently. In addition to its ICM activity, IcmF also catalyzes the interconversion of isovaleryl-CoA and pivalyl-CoA. This review focuses on the involvement of acyl-CoA mutases in central carbon and secondary bacterial metabolism and on their biotechnological potential for applications ranging from bioremediation to stereospecific synthesis of C2-C5 carboxylic acids and alcohols, and for production of potential commodity and specialty chemicals.
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Affiliation(s)
- Valentin Cracan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109-0600, USA
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