Evidence for an iterative module in chain elongation on the azalomycin polyketide synthase

Abstract

SummaryThe assembly-line synthases that produce bacterial polyketide natural products follow a modular paradigm in which each round of chain extension is catalysed by a different set or module of enzymes. Examples of deviation from this paradigm, in which a module catalyses either multiple extensions or none are of interest from both a mechanistic and an evolutionary viewpoint. We present evidence that in the biosynthesis of the 36-membered macrocyclic aminopolyol lactones (marginolactones) azalomycin and kanchanamycin, isolated respectively from Streptomyces malaysiensis DSM4137 and Streptomyces olivaceus Tü4018, the first extension module catalyses both the first and second cycles of polyketide chain extension. To confirm the integrity of the azl gene cluster, it was cloned intact on a bacterial artificial chromosome and transplanted into the heterologous host strain Streptomyces lividans, which does not possess the genes for marginolactone production. When furnished with 4-guanidinobutyramide, a specific precursor of the azalomycin starter unit, the recombinant S. lividans produced azalomycin, showing that the polyketide synthase genes in the sequenced cluster are sufficient to accomplish formation of the full-length polyketide chain. This provides strong support for module iteration in the azalomycin and kanchanamycin biosynthetic pathways. In contrast, re-sequencing of the gene cluster for biosynthesis of the polyketide β-lactone ebelactone in Streptomyces aburaviensis has shown that, contrary to a recently-published proposal, the ebelactone polyketide synthase faithfully follows the colinear modular paradigm.

Guanidine-Containing Polyhydroxyl Macrolides: Chemistry, Biology, and Structure-Activity Relationship

“…On the one hand, our group has been researching the practice and law of drug combinations to prevent antimicrobial resistance [5,6,7]; on the other, we have been trying our best to discover new antimicrobial agents. Guanidine-containing polyhydroxyl macrolides can be generally biosynthesized by many actinomycetes [8,9,10], and all these compounds contain a lactone ring and a guanidyl side chain. Azalomycin F, a complex including three main compounds, F 3a , F 4a , and F 5a , isolated from the broth of Streptomyces hygroscopicus var.…”

An Iterative Module in the Azalomycin F Polyketide Synthase Contains a Switchable Enoylreductase Domain

“…Azalomycin F5a and certain F5a derivatives also show anti‐MRSA activity 19. Azalomycins F3a, F4a, and F5a are also produced by Streptomyces malaysiensis DSM 4137,20 and we have previously proposed a model in which the first extension module catalyzes both the first and second cycles of polyketide chain extension, based on the observation that when the cluster is transplanted into a heterologous strain, azalomycins are produced, which rules out the participation of an additional PKS encoded elsewhere in the S. malaysiensis genome 21. Whole‐genome sequencing of Streptomyces sp.…”

The biosynthetic pathway to ossamycin, a macrocyclic polyketide bearing a spiroacetal moiety

“…Finally, the chain is transferred to the KS domain of module 11 for further processing. A number of examples of such programmed modular iteration have been previously described [49–52], although to our knowledge this is the first example of two malonate units being added by a single module.…”