Caerulomycin and collismycin antibiotics share a trans-acting flavoprotein-dependent assembly line for 2,2’-bipyridine formation

Abstract

Linear nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) template the modular biosynthesis of numerous nonribosomal peptides, polyketides and their hybrids through assembly line chemistry. This chemistry can be complex and highly varied, and thus challenges our understanding in NRPS and PKS-programmed, diverse biosynthetic processes using amino acid and carboxylate building blocks. Here, we report that caerulomycin and collismycin peptide-polyketide hybrid antibiotics share an assembly line that involves unusual NRPS activity to engage a trans-acting flavoprotein in C-C bond formation and heterocyclization during 2,2’-bipyridine formation. Simultaneously, this assembly line provides dethiolated and thiolated 2,2’-bipyridine intermediates through differential treatment of the sulfhydryl group arising from l-cysteine incorporation. Subsequent l-leucine extension, which does not contribute any atoms to either caerulomycins or collismycins, plays a key role in sulfur fate determination by selectively advancing one of the two 2,2’-bipyridine intermediates down a path to the final products with or without sulfur decoration. These findings further the appreciation of assembly line chemistry and will facilitate the development of related molecules using synthetic biology approaches.

Tracing of Acyl Carrier Protein-channeled Mitomycin Intermediates in Streptomyces caespitosus Facilitates Characterization of the Biosynthetic Steps for AHBA–GlcN Formation and Processing

“…22 Changes in ACP S-acylation can be examined based on an ejected Ppant-characteristic ion during MS/MS analysis. 23,24 As a result, two intermediates were revealed to be dominantly tethered on MmcB-I (Figures 3 and S4 and S5). Compared with AHBA−GlcNAc (2), one of the intermediates is a -42 Da product (3) that is consistent with the assignment to AHBA−GlcN by the loss of an acetyl group.…”

Investigation of 2,2′-Bipyridine Biosynthesis Reveals a Common Two-Component System for Aldehydes Production by Carboxylate Reduction

“…Caerulomycins (CAEs) and collismycins (COLs), the two groups of structurally related 2,2′-bipyridine antibiotics that differ from each other primarily by lacking or having sulfur decoration (Figure ), display a wide variety of biological properties such as anti-infection, cytotoxicity, immunosuppression, and neuron protection. − In line with their structural similarity, CAEs and COLs share the assembly line biogenesis of a modular polyketide synthase (PKS)/NRPS hybrid system, which templates the sequential incorporation of the same monomers picolinic acid, malonyl CoA, l -cysteine, and l -leucine. ,− Recently, we reported that this assembly line guides the formation of similar desulfurized (for CAEs) and sulfurized (for COLs) 2,2′-bipyridine intermediates with the association of a flavoprotein partner functioning in trans (Figure ). Subsequent l -leucine extension, which does not contribute any atoms to either CAEs or COLs, determines the fate of the different 2,2′-bipyridine intermediates, leading to the final products with or without sulfur decoration . Common post-PKS/NRPS modifications include the hydrolysis of the C-terminally extended leucinyl residue and the generation of a rarely found oxime functionality that is characteristic of both CAEs and COLs. ,,− During this process, the reductive conversion of the nascent carboxylic group into an aldehyde, which is necessary for the subsequent transamination and oxidation steps, remains to be elucidated (Figure ).…”

“…In contrast, omitting the LMW thiol CoA from the reaction mixtures had little effect, questioning the necessity of CoA-thiolation for CaeB2-catalyzed reduction (Figure S6). To clarify this point, we determined whether 2,2′-bipyridine-CoA ( 4 ) is an intermediate during carboxylate reduction. CaeB2 was incapable of using synthetic 4 ([M + H] + m / z : calcd.…”

“…26,28−30 Recently, we reported that this assembly line guides the formation of similar desulfurized (for CAEs) and sulfurized (for COLs) 2,2′-bipyridine intermediates with the association of a flavoprotein partner functioning in trans (Figure 1). 31 Subsequent L-leucine extension, which does not contribute any atoms to either CAEs or COLs, determines the fate of the different 2,2′-bipyridine intermediates, leading to the final products with or without sulfur decoration. 31 Common post-PKS/NRPS modifications include the hydrolysis of the C-terminally extended leucinyl residue and the generation of a rarely found oxime functionality that is characteristic of both CAEs and COLs.…”

“…31 Subsequent L-leucine extension, which does not contribute any atoms to either CAEs or COLs, determines the fate of the different 2,2′-bipyridine intermediates, leading to the final products with or without sulfur decoration. 31 Common post-PKS/NRPS modifications include the hydrolysis of the C-terminally extended leucinyl residue and the generation of a rarely found oxime functionality that is characteristic of both CAEs and COLs. 20,26,32−34 During this process, the reductive conversion of the nascent carboxylic group into an aldehyde, which is necessary for the subsequent transamination and oxidation steps, remains to be elucidated (Figure 1).…”