RESUMO
Through metabolic profiling of mutants and wild type of the endofungal bacterium Burkholderia rhizoxinica two novel rhizoxin derivatives with unusual nitrile substitutions were discovered. The nitrile groups result from a photochemical oxidative cleavage of the oxazolyl moiety. In vitro studies revealed that the photooxidation by singlet oxygen also takes place in the absence of a photosensitizer, and that also a thiazolyl-substituted rhizoxin analogue undergoes the same transformation. The resulting nitriles have antimitotic properties but are significantly less active than the parent compounds. These results highlight the impact of photoreactions onto the antiproliferative agent and encourage the introduction of bioisosteric groups that render the compound less susceptible towards photooxidation.
Assuntos
Antimitóticos/química , Antimitóticos/farmacologia , Macrolídeos/química , Macrolídeos/farmacologia , Nitrilas/química , Oxazóis/química , Processos Fotoquímicos , Antimitóticos/metabolismo , Linhagem Celular Tumoral , Humanos , Macrolídeos/metabolismoRESUMO
Trans-acyltransferase polyketide synthases (trans-AT PKSs) are an important group of bacterial enzymes producing bioactive polyketides. One difference from textbook PKSs is the presence of one or more free-standing AT-like enzymes. While one homolog loads the PKS with malonyl units, the function of the second copy (AT2) was unknown. We studied the two ATs PedC and PedD involved in pederin biosynthesis in an uncultivated symbiont. PedD displayed malonyl- but not acetyltransferase activity toward various acyl carrier proteins (ACPs). In contrast, the AT2 PedC efficiently hydrolyzed acyl units bound to N-acetylcysteamine or ACP. It accepted substrates with various chain lengths and functionalizations but did not cleave malonyl-ACP. These data are consistent with the role of PedC in PKS proofreading, suggesting a similar function for other AT2 homologs and providing strategies for polyketide titer improvement and biosynthetic investigations.
Assuntos
Aciltransferases/metabolismo , Policetídeos/metabolismo , Acetilcoenzima A/metabolismo , Bacillus/enzimologia , Malonil Coenzima A/metabolismo , Filogenia , Polienos/metabolismo , Piranos/metabolismoRESUMO
Chain armor against tumor cells: The oxazole side chain in the antimitotic agent rhizoxin S2 (1) was successfully replaced through mutasynthesis by using an engineered mutant impaired in heterocyclization. Incorporation of 12 non-natural surrogates into fully processed rhizoxin analogues revealed a remarkable substrate flexibility of the PKS-NRPS hybrid.
Assuntos
Antibióticos Antineoplásicos/metabolismo , Burkholderia/enzimologia , Burkholderia/genética , Macrolídeos/metabolismo , Oxazóis/metabolismo , Sequência de Aminoácidos , Antibióticos Antineoplásicos/química , Burkholderia/química , Burkholderia/metabolismo , Genes Fúngicos , Loci Gênicos , Macrolídeos/química , Dados de Sequência Molecular , Mutação , Oxazóis/química , Peptídeo Sintases/genética , Peptídeo Sintases/metabolismo , Policetídeo Sintases/genética , Policetídeo Sintases/metabolismoRESUMO
Targeted gene inactivation and metabolic profiling revealed that the cryptic PKS-NRPS gene cluster in the genome of the plant commensal Pseudomonas fluorescens Pf-5 codes for the biosynthesis of antiproliferative and antifungal rhizoxin derivatives.