Quinovosamycins: new tunicamycin-type antibiotics in which the α, β-1″,11′-linked N-acetylglucosamine residue is replaced by N-acetylquinovosamine

Abstract

Tunicamycins (TUN) are potent inhibitors of polyprenyl phosphate N-acetylhexosamine 1-phosphate transferases (PPHP), including essential eukaryotic GPT enzymes and bacterial HexNAc 1-P translocases. Hence, TUN blocks the formation of eukaryotic N-glycoproteins and the assembly of bacterial call wall polysaccharides. The genetic requirement for TUN production is well-established. Using two genes unique to the TUN pathway (tunB and tunD) as probes we identified four new prospective TUN-producing strains. Chemical analysis showed that one strain, Streptomyces niger NRRL B-3857, produces TUN plus new compounds, named quinovosamycins (QVMs). QVMs are structurally akin to TUN, but uniquely in the 1″,11'-HexNAc sugar head group, which is invariably d-GlcNAc for the known TUN, but is d-QuiNAc for the QVM. Surprisingly, this modification has only a minor effect on either the inhibitory or antimicrobial properties of QVM and TUN. These findings have unexpected consequences for TUN/QVM biosynthesis, and for the specificity of the PPHP enzyme family.

Exploring the Active Site of the Antibacterial Target MraY by Modified Tunicamycins

“…Interestingly, the inhibition of CbMraY as determined by the FRET-based activity assay is remarkably reduced by the modification, where QVM 16:1 ( iso ) is almost 100-fold less potent compared to the corresponding tunicamycin variant Tun 16:1 ( iso ). It has previously been shown that QVM inhibits S. cerevisiae GPT as potently as tunicamycin (MIC value of 0.25 μL/ml for both compounds) in a broth dilution assay . Hence, removal of the hydroxyl group on the 6″-carbon of the tunicamycin GlcNAc has a significantly different effect on MraY inhibition as compared to GPT inhibition.…”

“…The uracil ring-opened analog (TunR3) was prepared by base-catalyzed hydrolysis of TunR2 . Quinovosamycins were isolated from Streptomyces niger NRRL B-3857 as described . The compounds were purified by reversed-phase HPLC on a Finnigan Surveyor instrument (ThermoFisher Scientific, West Palm Beach, FL, USA) using a specialized C 30 column typically used to purify long-chain carotenes (YMC Carotene C-30, 3 μm particle size, 4.6 × 250 mm).…”

“…Homologues of tunicamycin can occur with different chain length N -acyl groups, and these fatty acyl chains can be further defined in terms of their terminal branching, either iso -, anteiso -, or unbranched − (this paper, Figure A). Variants of the typical tunicamycins have been reported including the quinovosamycins (QVM) produced by S. niger where the GlcNAc motif is replaced with QuiNAc (Figure B) . It has been shown that tunicamycin and QVM display similar minimum inhibitory concentration (MIC) values against the eukaryotic model system Saccharomyces cerevisiae , whereas tunicamycin is ∼10-fold more potent than QVM against Bacillus subtilis bacteria …”

“…Variants of the typical tunicamycins have been reported including the quinovosamycins (QVM) produced by S. niger where the GlcNAc motif is replaced with QuiNAc (Figure B) . It has been shown that tunicamycin and QVM display similar minimum inhibitory concentration (MIC) values against the eukaryotic model system Saccharomyces cerevisiae , whereas tunicamycin is ∼10-fold more potent than QVM against Bacillus subtilis bacteria …”

“…Variants of the typical tunicamycins have been reported including the quinovosamycins (QVM) produced by S. niger where the GlcNAc motif is replaced with QuiNAc (Figure 2B). 17 It has been shown that tunicamycin and QVM display similar minimum inhibitory concentration (MIC) values against the eukaryotic model system Saccharomyces cerevisiae, whereas tunicamycin is ∼10-fold more potent than QVM against Bacillus subtilis bacteria. 17 An important biological effect of tunicamycin initially reported by Walker et al is the dramatic synergy observed with β-lactam antibiotics, 18 although it has also been pointed out that natural tunicamycin is too toxic for clinical use.…”