New insights into the dihydro-mureidomycin biosynthesis controlled by two unusual proteins in Streptomyces roseosporus.

BACKGROUND

Uridyl peptide compounds are renowned as a subclass of nucleoside antibiotics for their highly specific antibacterial activity against Gram-negative bacteria and the unique target of action. We previously activated the biosynthetic gene cluster of a uridyl peptide antibiotic, mureidomycin, in Streptomyces roseosporus NRRL 15998 by introducing an exogenous positive regulator gene ssaA, and the generated strain was designated as Sr-hA. This study aims to further explore mureidomycin analogs from Sr-hA as well as the collaborative roles of two wide-spread genes, SSGG-02980 and SSGG-03002 encoding putative nuclease/phosphatase and oxidoreductase respectively, in mureidomycin diversification.

RESULTS

In order to understand how SSGG-02980 and SSGG-03002 contribute to mureidomycin biosynthesis, the gene disruption mutants and complementary strains were constructed. Mass spectrometry analyses revealed that two series of pairwise mureidomycin analogs were synthesized in Sr-hA with a two-dalton difference in molecular weight for each pair. By disruption of SSGG-03002, only mureidomycins with lower molecular weight (MRDs, 1-6) could be specifically accumulated in the mutant (∆03002-hA), whereas the other series of products with molecular weight plus 2 Da (rMRDs, 1'-6') became dominant in SSGG-02980 disruption mutant (∆02980-hA). Further comprehensive NMR analyses were performed to elucidate the structures, and three MRDs (3, 4, 5) with unsaturated double bond at C5-C6 of uracil group were characterized from ∆03002-hA. In contrast, the paired rMRDs analogs (3', 4', 5') from ∆SSGG-02980 corresponding to 3, 4 and 5 were shown to contain a single bond at this position. The results verified that SSGG-03002 participates in the reduction of uracil ring, whereas SSGG-02980 antagonizes the effect of SSGG-03002, which has been rarely recognized for a phosphatase.

CONCLUSIONS

Overall, this study revealed the key roles of two wide-spread families of enzymes in Streptomyces. Of them, oxidoreductase, SSGG-03002, is involved in dihydro-mureidomycin biosynthesis of S. roseosporus, whereas nuclease/phosphatase, SSGG-02980, has an adverse effect on SSGG-03002. This kind of unusual regulation model between nuclease/phosphatase and oxidoreductase is unprecedented, providing new insights into the biosynthesis of mureidomycins in Streptomyces. The findings would be of significance for structural diversification of more uridyl peptide antibiotics against Gram-negative bacteria.