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.
"The peptidyl nucleoside antibiotic nikkomycin, produced by Streptomyces ansochromogenes 7100  and Streptomyces tendae Tü 901 , 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]. "
[Show abstract][Hide abstract] 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.
"Nikkomycins are peptidyl nucleoside antibiotics that are produced by Streptomyces ansochromogenes and Streptomyces tenda (Ling et al., 2007; Lauer et al., 2001). As for many antibiotics, nikkomycin biosynthesis is dependent on growth phase and it is produced at stationary phase in SP liquid medium. "
[Show abstract][Hide abstract] ABSTRACT: Streptomyces ansochromogenes SanG is a pathway-specific regulator that mainly controls the transcription of two transcriptional units involved in nikkomycin biosynthesis. SanG consists of three major functional domains: an N-terminal Streptomyces antibiotic regulatory protein (SARP) domain, a central ATPase domain, and a C-terminal half homologous to guanylate cyclases belonging to the LuxR family. SanG was expressed in Escherichia coli as a C-terminally His(6)-tagged protein. The purified SanG-His( 6) was shown to be a dimer in solution by dynamic light scattering. An electrophoretic mobility-shift assay showed that the purified SanG protein could bind to the DNA fragment containing the bidirectional sanN-sanO promoter region. The SanG-binding sites within the bidirectional sanN-sanO promoter region were determined by footprinting analysis and identified a consensus-directed repeat sequence 5'-CGGCAAG-3'. SanG showed significant ATPase/GTPase activity in vitro, and addition of ATP/GTP enhanced the affinity of SanG for target DNA, but ATP/GTP hydrolysis was not essential for SanG binding to the target DNA. However, real-time reverse transcription PCR showed that mutation of the ATPase/GTPase domain of SanG significantly decreased the transcriptional level of sanN-I and sanO-V. These results indicated that the ATPase/GTPase activity of SanG modulated the transcriptional activation of SanG target genes during nikkomycin biosynthesis.
[Show abstract][Hide abstract] ABSTRACT: The term "adaptation" in the behavioral sciences refers to the ability of living tissue to adjust to the demands of environmental changes. This is accomplished in a variety of ways. For example, the sense organs become less sensitive when stimulated and more sensitive when stimulation is removed. Long-term effects of adaptation, for example to distracting noises, are observed in the absence of known physiological changes. The perceptual system is able to extract from the large quantity and quality of stimuli impinging upon it only those which are of interest and relevance. The prime mechanism of adaptation, however, is the ability of the human operator to adjust his responses to novel situations, i.e., learning It is the redundancy of the human operator which is his most valuable asset and prescribes the inclusion of the human in complex systems in spite of the concomitant demands for life support. The papers in the symposium are designed to illustrate several ways in which the human operator exhibits adaptation.
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