SanM catalyzes the formation of 4-pyridyl-2-oxo-4-hydroxyisovalerate in nikkomycin biosynthesis by interacting with SanN

State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 10/2007; 361(1):196-201. DOI: 10.1016/j.bbrc.2007.07.016
Source: PubMed


Nikkomycins are peptidyl nucleoside antibiotics with potent activities against phytopathogenic and human pathogenic fungi. The sanM and sanN genes are required for the nikkomycin biosynthesis of Streptomyces ansochromogenes. In the present study, interaction between SanM and SanN was identified by yeast two-hybrid and co-immunoprecipitation assays. Moreover, SanM and SanN were heterologously expressed and purified. Further biochemical assay demonstrated that the SanM-SanN interaction is essential for SanM aldolase activity but not for SanN dehydrogenase activity. SanM converts piconaldehyde and 2-oxobutyrate to 4-pyridyl-2-oxo-4-hydroxyisovalerate in nikkomycin biosynthesis by interacting with SanN. Steady state kinetics analysis revealed that K(m) and k(cat)/K(m) of SanM are 123.2 microM and 11.4 mM(-1)s(-1) for picolinaldehyde, while 335.6 microM and 4.0 mM(-1)s(-1) for 2-oxobutyrate, respectively. However, SanN as a dehydrogenase is independent of SanM.

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    • "The peptidyl nucleoside antibiotic nikkomycin, produced by Streptomyces ansochromogenes 7100 [17] and Streptomyces tendae Tü 901 [18], is a promising antibiotic against phytopathogenic fungi and human pathogens. In recent years, considerable progress has been made in understanding nikkomycin biosynthesis [13,17-21]. "
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    ABSTRACT: sabR is a pleiotropic regulatory gene which has been shown to positively regulate the nikkomycin biosynthesis and negatively affect the sporulation of Streptomyces ansochromogenes. In this study, we investigate the mechanism of SabR on modulating nikkomycin production in Streptomyces ansochromogenes. The transcription start point of sabR was determined by high-resolution S1 nuclease mapping and localized at the nucleotide T at position 37 bp upstream of the potential sabR translation start codon (GTG). Disruption of sabR enhanced its own transcription, but retarded the nikkomycin production. Over-expression of sabR enhanced nikkomycin biosynthesis in Streptomyces ansochromogenes. EMSA analysis showed that SabR bound to the upstream region of sanG, but it did not bind to the upstream region of its encoding gene (sabR), sanF and the intergenic region between sanN and sanO. DNase 1 footprinting assays showed that the SabR-binding site upstream of sanG was 5'-CTTTAAGTCACCTGGCTCATTCGCGTTCGCCCAGCT-3' which was designated as SARE. Deletion of SARE resulted in the delay of nikkomycin production that was similar to that of sabR disruption mutant. These results indicated that SabR modulated nikkomycin biosynthesis as an enhancer via interaction with the promoter region of sanG, and expanded our understanding about regulatory cascade in nikkomycin biosynthesis.
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    ABSTRACT: Nikkomycins are a group of peptidyl nucleoside antibiotics with potent fungicidal, insecticidal, and acaricidal activities. sanN was cloned from the partial genomic library of Streptomyces ansochromogenes 7100. Gene disruption and complementation analysis demonstrated that sanN is essential for nikkomycin biosynthesis in S. ansochromogenes. Primer extension assay indicated that sanN is transcribed from two promoters (sanN-P1 and sanN-P2), and sanN-P2 plays a more important role in nikkomycin biosynthesis. Purified recombinant SanN acts as a dehydrogenase to convert benzoate-CoA to benzaldehyde in a random-order mechanism in vitro, with respective Kcat/Km values of 3.8 mM-1s-1 and 12.0 mM-1s-1 toward benzoate-CoA and NADH, suggesting that SanN catalyzes the formation of picolinaldehyde during biosynthesis of nikkomycin X and Z components in the wild-type stain. These data would facilitate us to understand the biosynthetic pathway of nikkomycins and to consider the combinatorial synthesis of novel antibiotic derivatives.
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