Two Biosynthetic Pathways in Jahnella thaxteri for Thaxteramides

Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Two Biosynthetic Pathways in Jahnella thaxteri for Thaxteramides, Distinct Types of Lipopeptides Emilia Oueis,†,§ Thorsten Klefisch,†,§ Nestor Zaburannyi,† Ronald Garcia,†,‡ Alberto Plaza,† and Rolf Müller*,†,‡ †

Department of microbial natural products, Helmholtz-institute for pharmaceutical research Saarland (HIPS), Helmholtz center for infection research (HZI), Campus E8.1, 66123 Saarbrücken, Germany ‡ German Centre for Infection Research (DZIF), Partner Site Hannover, 38124 Braunschweig, Germany

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S Supporting Information *

ABSTRACT: The structures of five linear lipopeptides, thaxteramides A1, A2, B1, B2, and C isolated from the myxobacterium Jahnella thaxteri, were elucidated. They have a C-terminal common tetrapeptidic Tyr-Gly-β-Ala-Tyr core but differ in the stereochemistry of the tyrosine units, methylations, the remaining amino acids, and the N-terminal polyketide. In silico analysis of the genome sequence complemented with feeding experiments revealed two distinct hybrid PKS/NRPS gene clusters. Three semisynthesized cyclic analogues were found to inhibit the growth of Gram-positive bacteria.

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atural products are a rich source of biologically active compounds.1 Myxobacteria in particular have provided a constant supply of structurally interesting secondary metabolites with various biological activities.2,3 However, the discovery of new bioactive scaffolds has been increasingly challenging due to high rediscovery rates. Nonetheless, the chemical space diversity offered by nature is far from being understood.4,5 This is evidenced by the wide gap between isolated compounds and genome sequence analysis, due to the presence of the so-called silent genes, or compounds produced in small amounts that are overlooked in the isolation process.4,5 Different approaches varying in complexity are currently used to mine chemical novelty from natural resources. These include focusing on underexplored species, biological prioritization, improved analytical tools, and genomics, metagenomics, and bioengineering strategies.5−11 A previous NMR-based study of the Jahnella thaxteri MSr913912 strain had identified the presence of the known peptides microsclerodermin D and pedein A and led to the discovery of jahnellamides.13 Upon further LC-HRMS analysis of MSr9139 and comparison with known myxobacterial natural products based on accurate mass, retention time, and MS2 fragmentation analysis, new peptidic scaffolds were identified. MS2 analysis of the three major peaks indicated a common tetrapeptidic structure, Tyr-Gly-β-Ala-Tyr, which helped identify three additional minor derivatives. The most abundant derivative, thaxteramide A1 (ThxA1), displayed a HRMS peak at m/z 904.4463 [M + H]+ indicating a molecular formula of C46H61N7O12 with 20 degrees of unsaturation (Figure 1). The HSQC spectrum showed signals of two olefinic methines, 13 aromatic methines, eight aliphatic methines, seven methylenes, and four methyls, exhibiting © XXXX American Chemical Society

Figure 1. Structures of isolated thaxteramide derivatives.

signals characteristic of a peptide containing aromatic and oxygenated residues. The HMBC spectrum showed the 12 remaining quaternary carbons, seven of which are carbonyls and five of which are quaternary olefinic/aromatic carbons. This has been deduced on the basis of their 13C chemical shifts and HMBC correlations. Analysis of the COSY and TOCSY correlations revealed two tyrosines (Tyr), Me-β-alanine (AIB), glycine (Gly), serine (Ser), threonine (Thr), and the spin system of a branched unsaturated lipid chain (Lp1) with a terminal phenyl group. One of the tyrosines is O-methylated. On the basis of HMBC correlations and MS2 analysis, the sequence was identified as Lp1-Ser-Thr-O-MeTyr-Gly-AIBTyr. The double-bond configuration within the lipid chain was determined as E, based on the large coupling constant (J = 15.8 Hz). The absolute configurations of D-Tyr, L-Ser, and LReceived: April 30, 2019

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DOI: 10.1021/acs.orglett.9b01524 Org. Lett. XXXX, XXX, XXX−XXX

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Figure 2. (A) Putative gene cluster of thaxteramides A and B and their proposed biosynthetic pathway. (B) Prediction of the substrate specificity of the AT and A domains.

of the COSY and TOCSY correlations revealed the spin system of a branched unsaturated lipid chain (Lp2), two tyrosine units, β-alanine, glycine, and asparagine (Asn). On the basis of HMBC correlations and MS2 measurements, the sequence was identified as Lp2-Asn-Tyr-Gly-β-Ala-Tyr. On the basis of the NOESY correlation of CH3-10 with CH-11, the configuration of the double bond within Lp2 was determined to be Z. The absolute configurations of L-Tyr and L-Asn were assigned using Marfey’s method. The configuration of the two chiral centers of Lp2 was not determined experimentally. Thaxteramide D showed a much lower molecular weight (m/z 473.20352 [M + H]+) and a molecular formula of C23H28N4O7, indicating 12 degrees of unsaturation. ThxD has simple NMR spectra, displaying only the common tetrapeptide Tyr-Gly-β-Ala-Tyr. Marfey’s analysis showed that the tyrosines are L-configured, similar to ThxC. With the structure of thaxteramide derivatives in hand, we set to identify their biosynthetic pathway using a combination of feeding experiments and in silico analysis of the genome sequence of MSr9139. The feeding experiments were all analyzed by LC-MS (Table S23). The results showed the incorporation of [2H7]cinnamic acid (57−66%) and [2H5]phenylalanine (63−73%) within all A and B derivatives. [2H3]Me-Malonic acid was incorporated once into ThxA and ThxB (32−34%) and twice (38% and 17%) into ThxC, indicating the incorporation of one and two units of methyl malonate, respectively. Feeding with either [13C5,15N2]glutamine, [13C4,15N2]asparagine, or [13C4,15N]aspartic acid resulted in a cluster of ions with 1 Da additions, which is composed of randomly reassembled fragments of the 13C- and 15 N-labeled amino acids. In the case of [13C4,15N2]asparagine, however, a clear full incorporation within ThxC could also be

Thr were assigned by Marfey’s method, and that of 2(R)-AIB was assigned by comparison to a synthetic 2(S)-AIB sample.14 Both (R)- and (S)-ThxA1-Mosher amides were synthesized, and the relevant proton chemical shifts compared, and the Lp1-C3 stereochemistry (amine) was determined to be R (Table S22).15 The Lp1-C4 stereochemistry could not be determined using NMR methods;16 nonetheless, the absolute stereochemistry was tentatively assigned as 3R,4S, supported by in silico analysis, and is discussed further below. Thaxteramide B1 showed an ion peak at m/z 890.4292 [M + H]+ (C45H59N7O12) that is 14 mass units lower than that of ThxA1. The NMR data closely resembled those of ThxA1 with the exception that the methyl group of AIB was missing and replaced by β-Ala. Marfey’s analysis indicated the same configuration as for ThxA1. The minor derivatives, thaxteramide A2 and B2, both showed a 14 mass unit difference with A1 and B1, respectively. Both ThxA2 with an ion peak at m/z 890.42856 [M + H]+ (C45H59N7O12) and ThxB2 with an ion peak at m/z 876.41290 [M + H]+ (C44H57N7O12) are missing the O-methyl singlet on the tyrosine. Despite similarities in the C-terminal peptidic part, thaxteramide C was structurally different from ThxA/B. ThxC displayed a HRMS peak at m/z 782.40859 [M + H]+ indicating a molecular formula of C39H55N7O10 with 16 degrees of unsaturation. The HSQC spectrum showed signals of one olefinic methine, eight aromatic methines, five aliphatic methines, 10 methylenes, and three methyls. The HMBC spectrum showed the 11 remaining quaternary carbons, seven of which are carbonyls and four of which are quaternary olefinic/aromatic carbons. This has been deduced on the basis of their 13C chemical shifts and HMBC correlations. Analysis B


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Figure 3. (A) Putative gene cluster of thaxteramide C and its proposed biosynthetic pathway. (B) Prediction of the substrate specificity of AT and A domains.

observed. On the other hand, feeding with [15N]glutamic acid clearly indicated the incorporation of the labeled nitrogen atom (52−57%), confirming the origin of the amino group on the lipid chains. The intact incorporation of up to two L[2H4]tyrosine units in all compounds (18−25% and 62−74%) indicates that epimerization of Tyr in ThxA and B derivatives occurs separately. Feeding with [Me-2H3]methionine showed only one methyl incorporation in ThxA1 and ThxB1 exclusively, accounting for the O-methylation of the tyrosine. This result also eliminates the possibility of a C-methylation of β-Ala in ThxB to generate AIB and the corresponding ThxA derivatives. Hence, it is assumed that both β-Ala and AIB are incorporated through the corresponding NRPS module. On the basis of the elucidated chemical structures of the thaxteramide lipopeptides and the feeding results, we hypothesized that ThxA/B and ThxC derivatives are assembled by two distinct hybrid NRPS/PKS gene clusters. Upon investigation of the genome sequence of MSr9139 using anti-SMASH,17 indeed, two distinct gene clusters were identified as being responsible for thaxteramide biosynthesis. The predicted substrate specificity for most PKS18 and NRPS modules19 within each cluster, as well as the identified additional domains, was in line with the determined structures of the respective thaxteramides and the results from the feeding experiments. ThxA and ThxB derivatives are biosynthesized by the gene cluster thxA, ∼56 kb in size and comprising 15 putative open reading frames (ORFs), including the bimodular PKS thxA1 and the heptamodular PKS/NRPS thxA2 (Figure 2). It is noteworthy that, given that Jahnella sp. is not accessible for genetic manipulation, the exact boundaries of the gene cluster could not be determined experimentally. The assembly of ThxA and ThxB starts with the activation of trans-cinnamic acid by CoA ligase and condensation to methyl malonate,

which is subsequently reduced. The polyketide fragment is then transferred onto module 3, where malonyl-CoA is incorporated and its β-keto function subjected to a transamination reaction by the C-terminal aminotransferase (AMT) domain. Subsequently, the sequential incorporation of Ser, Thr, Tyr, Gly, β-Ala/AIB, and Tyr proceeds via the remaining NRPS modules 4−9. Epimerization domains in modules 6 and 9 confirm the presence of D-tyrosines. The O-methyl group on the first tyrosine unit results from a SAM-dependent methyltransferase (MT) as indicated by the feeding experiment with labeled methionine, which we assume is present as an uncommon domain in module 6. In silico analysis of its amino acid sequence and structural homology models20 highlights an unprecedented MT domain in natural product assembly lines, suggesting it is related to histone arginine methyltransferases21 rather than the commonly observed type I MT domains.22 The methylated form, even though most abundant, is not exclusive. Hence, the lack of methylation seems not to impede subsequent recognition, as confirmed by the presence of the minor derivatives ThxA2 and ThxB2. Finally, the lipopeptide is released through an unusual condensation domain in module 9 and not the regular thioesterase (TE) domain, similar to what was reported for the biosynthesis of crocacin.23 However, a phylogenetic analysis shows that the two terminal C domains are not very similar.24 ThxC is biosynthesized by the gene cluster thxC that is ∼79 kb in size and includes 26 ORFs, among them the trimodular PKS gene thxC1 and the hexamodular hybrid NRPS/PKS gene thxC2 (Figure 3). The precise boundaries of the gene cluster could again not be determined. Interestingly, module 1 is a mixed loading and extension module, where the starter unit (acetyl-CoA) is loaded from the first AT to the first ACP and the extension unit (methylmalonate) from the second AT to C


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β-Ala has been reconfirmed;31 however, the difference in the specificity for β-Ala and AIB could not be pinpointed. The natural linear thaxteramide derivatives showed no antifungal, antibacterial, or cytotoxic activities. We speculated that the compounds might be active as cyclic lipopeptides;32 however, the cyclic derivatives were never detected in the crude extract. To evaluate their activity, thaxteramides A1, B1, and C were macrocyclized in good yields by coupling the Cterminal carboxylic acid to the free amine on the lipid chain using HATU as the coupling reagent in the presence of DIEA in DMSO at room temperature overnight. The resulting cyclic lipopeptides cyc-ThxA, cyc-ThxB, and cyc-ThxC were purified and fully characterized. Cyc-ThxA and cyc-ThxC showed an interesting activity against Bacillus subtilis, Staphylococcus aureus Newman, and Streptococcus pneumoniae with MIC values between 4 and 32 μg/mL. Furthermore, preliminary investigations show that both cyclic lipopeptides exhibit significant inhibition of some daptomycin- and methicillinresistant S. aureus strains (Figure 4).

the second ACP, as is the case in the chondramide biosynthetic gene cluster25 and other myxobacterial compounds.26−29 The specificity of the first AT domain (AT1a) shifts to a monocarboxylic acid due to the presence of Ala200 and Trp117 in its sequence.18 For the double bond to be formed, both KR and DH domains are required. The latter is absent in module 1, but this function could be accomplished by any potential iterative DH domain from other modules. The polyketide chain is then extended by a reduced malonate, contrary to what was predicted for AT2. This has also been observed in the biosynthesis of myxalamide.27 This is followed successively by a reduced methylmalonate and a malonate that undergoes a transamination similar to that of ThxA/B. The polyketide is then extended by NRPS modules 5−9 with Asn, Tyr, Gly, β-Ala, and Tyr, all as L-amino acids. The linear lipopeptide ThxC is finally released by hydrolysis through a terminal TE domain. Given the stereochemistry of the tyrosine units in ThxD and the absence of a specific tetrapeptide encoding NRPS gene cluster within the MSr9139 sequenced genome, it is likely that it has arisen from gene duplication of the relevant parts of thxC. Five ORFs located upstream of thxC1 have been identified as being involved with reductive pyrimidine metabolism and could explain the biosynthetic origin of the β-Ala and AIB incorporated into thaxteramides. Uracil is first converted to 5,6-dihydrouracil by dihydopyrimidine dehydrase (ORFs 6 and 7), after which dihydropyrimidinase (ORF 5) catalyzes its reversible hydrolytic ring opening to N-carbamoyl-β-Ala, followed by hydrolysis to β-Ala by β-ureidopropionase (ORF 4). Similarly, thymine is catabolized into AIB. Additional feeding experiments with isotopically labeled [2H2]uracil and [2H4]thymine have been conducted. As expected, labeled β-Ala (1 and 2 Da) is detected within ThxB1 (39% and 34%), ThxB2 (24% and 43%), and ThxC (40% and 31%) after feeding with uracil. Unexpectedly, the deuterated methyl group from thymine seemed to be incorporated once or twice in all derivatives, ThxA1 (36% and 54%), ThxA2 (37% and 52%), ThxB1 (12%), ThxB2 (16%), and ThxC (37% and 26%). Further MS2 analysis showed the unexpected incorporation results from methylmalonate units, with the expected incorporation of labeled AIB exclusively in ThxA1 and ThxA2. Indeed, further catabolism of AIB generates methylmalonate through methylmalonate semialdehyde, by the reaction of a transaminase and a methylmalonate semialdehyde dehydrogenase, the latter of which is encoded in ORF 3. Among the remaining ORFs in both gene clusters, no obvious correlations with secondary metabolism were identified. Further in silico analysis of the ER domains in modules 2 and 3 of thxA1 and thxC1, respectively, and comparison to known ER domains from PKS genes indicated that the stereochemistry at the C4 center of both lipid chains of ThxA and C derivatives is (S)-configured. Indeed, the stereochemistry of the corresponding methyl group resulting from a methylmalonate extension depends on the stereospecificity of the ER domain reduction of the 2-enoyl intermediate. It has been previously shown that the presence of the conserved residue Y85 within the ER domain results in a 2(S) configuration at the reduction site (Figure S12).30 This result combined with NMR strongly indicates that the stereochemistry on the lipid chain is (3R,4S) and is assumed to be the same for all derivatives. Additionally, the observation that the usually conserved Asp235 in A domains is shifted to position 236 for

Figure 4. Structures of the semisynthetic cyclized thaxteramides.

In summary, thaxteramides are a new linear lipopetide scaffold that contains a common C-terminal tetrapeptide, TyrGly-β-Ala-Tyr, where the β-Ala in ThxA derivatives is replaced with AIB and the first Tyr is O-methylated in ThxA1 and ThxB1. The stereochemistry of the Tyr differs between A/B and C derivatives. One or two amino acids then extend the peptide into an N-terminal lipid chain, which is different between ThxA/B and ThxC but holds the same 3-amino-4methyl carboxylic acid fragment. A tentative stereochemical assignment has been done using the modified Mosher method on ThxA1 and complemented with in silico analysis and indicates a (3R,4S)-3-amino-4-methyl fragment. Given the high level of sequence identity of the corresponding AMT domains (75%) of ThxA and ThxC, and in silico analysis of the ER domain of both, the stereochemistry of the lipid chain in ThxC is assumed to be the same. The absolute stereochemical assignment of both could further be verified by total synthesis. Not surprisingly, thaxteramides are synthesized by two distinct hybrid PKS/NRPS biosynthetic gene clusters as demonstrated by in silico analysis and feeding experiments. The case of thaxteramides is fairly similar to that of microsclerodermin and pedein, both synthesized by J. thaxteri MSr9139, as their overall structures are closely related while they have emerged from related but distinct biosynthetic gene clusters.33 Even though the natural thaxteramides showed no activity in the assays performed, the cyclic derivatives cyc-ThxA and cycThxC were active against some Gram-positive bacteria and most notably S. aureus resistant strains. These results warrant further synthetic development of thaxteramides and more studies of their mode of action as cyclic lipopetides. D


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(13) Plaza, A.; Viehrig, K.; Garcia, R.; Müller, R. Jahnellamides, αKeto-β-Methionine-Containing Peptides from the Terrestrial Myxobacterium Jahnella sp.: Structure and Biosynthesis. Org. Lett. 2013, 15, 5882−5885. (14) Oueis, E.; Stevenson, H.; Jaspars, M.; Westwood, N. J.; Naismith, J. H. Bypassing the proline/thiazoline requirement of the macrocyclase PatG. Chem. Commun. 2017, 53, 12274−12277. (15) Hoye, T. R.; Jeffrey, C. S.; Shao, F. Mosher ester analysis for the determination of absolute configuration of stereogenic (chiral) carbinol carbons. Nat. Protoc. 2007, 2, 2451−8. (16) Matsumori, N.; Kaneno, D.; Murata, M.; Nakamura, H.; Tachibana, K. Stereochemical Determination of Acyclic Structures Based on Carbon-Proton Spin-Coupling Constants. A Method of Configuration Analysis for Natural Products. J. Org. Chem. 1999, 64, 866−876. (17) Blin, K.; Weber, T.; Kim, H. U.; Lee, S. Y.; Medema, M. H.; Duddela, S.; Krug, D.; Müller, R.; Bruccoleri, R.; Fischbach, M. A.; Wohlleben, W.; Takano, E.; Breitling, R. antiSMASH 3.0a comprehensive resource for the genome mining of biosynthetic gene clusters. Nucleic Acids Res. 2015, 43, W237−W243. (18) Yadav, G.; Gokhale, R. S.; Mohanty, D. Computational approach for prediction of domain organization and substrate specificity of modular polyketide synthases. J. Mol. Biol. 2003, 328, 335−363. (19) Stachelhaus, T.; Mootz, H. D.; Marahiel, M. A. The specificityconferring code of adenylation domains in nonribosomal peptide synthetases. Chem. Biol. 1999, 6, 493−505. (20) Kelley, L. A.; Mezulis, S.; Yates, C. M.; Wass, M. N.; Sternberg, M. J. E. The Phyre2 web portal for protein modeling, prediction and analysis. Nat. Protoc. 2015, 10, 845−858. (21) Cura, V.; Marechal, N.; Troffer-Charlier, N.; Strub, J. M.; van Haren, M. J.; Martin, N. I.; Cianferani, S.; Bonnefond, L.; Cavarelli, J. Structural studies of protein arginine methyltransferase 2 reveal its interactions with potential substrates and inhibitors. FEBS J. 2017, 284, 77−96. (22) Ansari, M. Z.; Sharma, J.; Gokhale, R. S.; Mohanty, D. In silico analysis of methyltransferase domains involved in biosynthesis of secondary metabolites. BMC Bioinf. 2008, 9, 454. (23) Müller, S.; Rachid, S.; Hoffmann, T.; Surup, F.; Volz, C.; Zaburannyi, N.; Müller, R. Biosynthesis of Crocacin Involves an Unusual Hydrolytic Release Domain Showing Similarity to Condensation Domains. Chem. Biol. 2014, 21, 855−865. (24) Rausch, C.; Hoof, I.; Weber, T.; Wohlleben, W.; Huson, D. H. Phylogenetic analysis of condensation domains in NRPS sheds light on their functional evolution. BMC Evol. Biol. 2007, 7, 78−78. (25) Rachid, S.; Krug, D.; Kunze, B.; Kochems, I.; Scharfe, M.; Zabriskie, T. M.; Blöcker, H.; Müller, R. Molecular and Biochemical Studies of Chondramide FormationHighly Cytotoxic Natural Products from Chondromyces crocatus Cm c5. Chem. Biol. 2006, 13, 667−681. (26) Gaitatzis, N.; Silakowski, B.; Kunze, B.; Nordsiek, G.; Blocker, H.; Hofle, G.; Muller, R. The biosynthesis of the aromatic myxobacterial electron transport inhibitor stigmatellin is directed by a novel type of modular polyketide synthase. J. Biol. Chem. 2002, 277, 13082−13090. (27) Silakowski, B.; Nordsiek, G.; Kunze, B.; Blöcker, H.; Müller, R. Novel features in a combined polyketide synthase/non-ribosomal peptide synthetase: the myxalamid biosynthetic gene cluster of the myxobacterium Stigmatella aurantiaca Sga1511This article is dedicated to Prof. Dr. E. Leistner on the occasion of his 60th birthday. Chem. Biol. 2001, 8, 59−69. (28) Silakowski, B.; Schairer, H. U.; Ehret, H.; Kunze, B.; Weinig, S.; Nordsiek, G.; Brandt, P.; Blocker, H.; Hofle, G.; Beyer, S.; Muller, R. New lessons for combinatorial biosynthesis from myxobacteria. The myxothiazol biosynthetic gene cluster of Stigmatella aurantiaca DW4/ 3−1. J. Biol. Chem. 1999, 274, 37391−37399. (29) Weinig, S.; Hecht, H.-J.; Mahmud, T.; Müller, R. Melithiazol Biosynthesis: Further Insights into Myxobacterial PKS/NRPS

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.9b01524.

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Experimental details, 1H and 13C assignments, MS and MS2 data, Marfey’s and feeding results, in silico analysis, and one- and two-dimensional NMR spectra (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Emilia Oueis: 0000-0002-0228-6394 Rolf Müller: 0000-0002-1042-5665 Author Contributions §

E.O. and T.K. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank HIPS colleagues Dr. K. Harmrolfs and Dr. L. Keller for NMR advice, Mr. J. Hug, Mr. F. Panter, and Mr. B. Schnell for insightful discussions, and Ms. V. Schmidt and Dr. J. Hermann for bioassays. This work was funded by the German Centre for Infection Research (DZIF).

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REFERENCES

(1) Katz, L.; Baltz, R. H. Natural product discovery: past, present, and future. J. Ind. Microbiol. Biotechnol. 2016, 43, 155−176. (2) Herrmann, J.; Fayad, A. A.; Müller, R. Natural products from myxobacteria: novel metabolites and bioactivities. Nat. Prod. Rep. 2017, 34, 135−160. (3) Gemperlein, K.; Zaburannyi, N.; Garcia, R.; La Clair, J. J.; Mü ller, R. Metabolic and Biosynthetic Diversity in Marine Myxobacteria. Mar. Drugs 2018, 16, 314−329. (4) Pye, C. R.; Bertin, M. J.; Lokey, R. S.; Gerwick, W. H.; Linington, R. G. Retrospective analysis of natural products provides insights for future discovery trends. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 5601−5606. (5) Harvey, A. L.; Edrada-Ebel, R.; Quinn, R. J. The re-emergence of natural products for drug discovery in the genomics era. Nat. Rev. Drug Discovery 2015, 14, 111−129. (6) Panter, F.; Krug, D.; Baumann, S.; Müller, R. Self-resistance guided genome mining uncovers new topoisomerase inhibitors from myxobacteria. Chem. Sci. 2018, 9, 4898−4908. (7) Zhang, M. M.; Qiao, Y.; Ang, E. L.; Zhao, H. Using natural products for drug discovery: the impact of the genomics era. Expert Opin. Drug Discovery 2017, 12, 475−487. (8) Ziemert, N.; Alanjary, M.; Weber, T. The evolution of genome mining in microbes − a review. Nat. Prod. Rep. 2016, 33, 988−1005. (9) Cieśla, Ł.; Moaddel, R. Comparison of analytical techniques for the identification of bioactive compounds from natural products. Nat. Prod. Rep. 2016, 33, 1131−1145. (10) Luo, Y.; Cobb, R. E.; Zhao, H. Recent advances in natural product discovery. Curr. Opin. Biotechnol. 2014, 30, 230−237. (11) Hoffmann, T.; Krug, D.; Hüttel, S.; Müller, R. Improving Natural Products Identification through Targeted LC-MS/MS in an Untargeted Secondary Metabolomics Workflow. Anal. Chem. 2014, 86, 10780−10788. (12) J. thaxteri strain SBSr007 is the same as MSr9139. MSr9139 will be used in this paper. E


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Organic Letters Systems and Evidence for a New Subclass of Methyl Transferases. Chem. Biol. 2003, 10, 939−952. (30) Kwan, D. H.; Sun, Y.; Schulz, F.; Hong, H.; Popovic, B.; SimStark, J. C. C.; Haydock, S. F.; Leadlay, P. F. Prediction and Manipulation of the Stereochemistry of Enoylreduction in Modular Polyketide Synthases. Chem. Biol. 2008, 15, 1231−1240. (31) Challis, G. L.; Ravel, J.; Townsend, C. A. Predictive, structurebased model of amino acid recognition by nonribosomal peptide synthetase adenylation domains. Chem. Biol. 2000, 7, 211−224. (32) Schneider, T.; Müller, A.; Miess, H.; Gross, H. Cyclic lipopeptides as antibacterial agents − Potent antibiotic activity mediated by intriguing mode of actions. Int. J. Med. Microbiol. 2014, 304, 37−43. (33) Hoffmann, T.; Müller, S.; Nadmid, S.; Garcia, R.; Müller, R. Microsclerodermins from Terrestrial Myxobacteria: An Intriguing Biosynthesis Likely Connected to a Sponge Symbiont. J. Am. Chem. Soc. 2013, 135, 16904−16911.

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Two Biosynthetic Pathways in Jahnella thaxteri for Thaxteramides

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