Antibacterial Muraymycins from Mutant Strains of Streptomyces sp. NRRL 30471

Abstract

Muraymycins are nucleoside antibiotics isolated from Streptomyces sp. NRRL 30471 and several mutant strains thereof that were generated by random, chemical mutagenesis. Reinvestigation of two mutant strains using new media conditions led to the isolation of three new muraymycin congeners, named B8, B9, and C6 (1-3), as well as a known muraymycin, C1. Structures of the compounds were elucidated by HRMS and 1D and 2D NMR spectroscopic analyses. Complete 2D NMR assignments for the known muraymycin C1 are also provided for the first time. Compounds 1 and 2, which differ from other muraymycins by having an elongated, terminally branched fatty acid side chain, had picomolar IC values against Staphylococcus aureus and Aquifex aeolicus MraY and showed good antibacterial activity against S. aureus (MIC = 2 and 6 μg/mL, respectively) and Escherichia coli Δ tolC (MIC = 4 and 2 μg/mL, respectively). Compound 3, which is characterized by an N-acetyl modification of the primary amine of the dissacharide core that is shared among nearly all of the reported muraymycin congeners, greatly reduced its inhibitory and antibacterial activity compared to nonacylated muraymycin C1, which possibly indicates this modification is used for self-resistance.

Insights into the Target Interaction of Naturally Occurring Muraymycin Nucleoside Antibiotics

“…Antibacterial activities of muraymycins against a range of pathogens have been reported before, [8c,9a,b] so we mainly aimed to confirm some of the previously reported data and to comparatively study activities against an efflux-deficient bacterial strain. In our hands, muraymycin A1 3 was the only congener with notable activity against S. aureus , which was in good agreement with previously published data.…”

“…In our hands, muraymycin A1 3 was the only congener with notable activity against S. aureus , which was in good agreement with previously published data. [9a,b] This result was remarkable though as muraymycins 3 – 6 all showed very similar inhibitory potencies towards MraY, thus indicating that the unique activity of 3 is correlated to cellular access to the target. We have reported a model system to study the membrane-interacting properties of the ω-functionalized fatty acid moiety of A-series muraymycins such as 3 , indicating both an efficient membrane accumulation and penetration mediated by the guanidinium-containing structural motif.…”

“…in 2002. [9] The muraymycin scaffold consists of a (5′ S ,6′ S )-glycyluridine (GlyU) core structure, which is connected to a peptide moiety by an alkyl linker. In most muraymycins, this core is 5′- O -aminoribosylated to generate an unusual disaccharide.…”

“…The originally isolated, naturally occurring muraymycins were solely assessed by their inhibition of the formation of lipid II (i.e., the biosynthetic intermediate following lipid I 2 ) and peptidoglycan in coupled assays, thus only indirectly supporting MraY inhibition. [9a,b] These assays revealed inhibition of lipid II and peptidoglycan formation at concentrations as low as 0.27 μg/mL, being equivalent to the low nM range. However, quantitative information on direct MraY inhibition remains unknown.…”

“…Using modified fermentation conditions based partly on previously reported methods, [9a,b] Streptomyces sp. (NRRL30473 for isolation of muraymycins A1 3 , B2 4 and B6 5 ; NRRL30475 for isolation of muraymycins D1 7 and D2 8 ; NRRL30477 for isolation of muraymycin C1 6 ) were cultivated for production.…”