Identification of stsC , the gene encoding the l -glutamine: scyllo -inosose aminotransferase from streptomycin-producing Streptomycetes

Abstract

Eight new genes, strO-stsABCDEFG, were identified by sequencing DNA in the gene cluster that encodes proteins for streptomycin production of Streptomyces griseus N2-3-11. The StsA (calculated molecular mass 43.5 kDa) and StsC (45.5 kDa) proteins - together with another gene product, StrS (39.8 kDa), encoded in another operon of the same gene cluster - show significant sequence identity and are members of a new class of pyridoxal-phosphate-dependent aminotransferases that have been observed mainly in the biosynthetic pathways for secondary metabolites. The aminotransferase activity was demonstrated for the first time by identification of the overproduced and purified StsC protein as the L-glutamine:scyllo-inosose aminotransferase, which catalyzes the first amino transfer in the biosynthesis of the streptidine subunit of streptomycin. The stsC and stsA genes each hybridized specifically to distinct fragments in the genomic DNA of most actinomycetes tested that produce diaminocyclitolaminoglycosides. In contrast, only stsC, but not stsA, hybridized to the DNA of Streptomyces hygroscopicus ssp. glebosus, which produces the monoaminocyclitol antibiotic bluensomycin; this suggests that both genes are specifically used in the first and second steps of the cyclitol transamination reactions. Sequence comparison studies performed with the deduced polypeptides of the genes adjacent to stsC suggest that the enzymes encoded by some of these genes [strO (putative phosphatase gene), stsB (putative oxidoreductase gene), and stsE (putative phosphotransferase gene)] also could be involved in (di-)aminocyclitol synthesis.

Biosynthetic genes for aminoglycoside antibiotics

“…41 However, not so many biosynthetic enzymes have been characterized even now because, probably, the biosynthetic pathway for streptomycin is too unique to predict appropriate functions compared with other aminoglycoside biosynthetic genes. Among the streptomycin biosynthetic enzymes, Gln:scyllo-inosose aminotransferase StsC 15 and Arg:inosamine-phosphate amidinotransferase StrB1 16 are characterized biochemically. Characterization of StsC was important, as described in the Introduction section, and thus led to the characterization of Gln:2DOI aminotransferase BtrS in the 2DOS biosynthesis.…”

“…[15][16][17][18] Among those, the characterization of L-glutamine: syllo-inosamine aminotransferase StsC gave important information to elucidate the aminocyclitol-containing aminoglycosides biosynthetic pathway. 15 Using the hybridization method, Piepersberg and co-workers 15 showed that its homologous gene is conserved in the aminocyclitol antibiotic-producing microorganisms. In fact, StsC homologous aminotransferase genes are conserved completely in the genomes of aminocyclitol antibiotic-producing microorganisms as a specific feature.…”

Identification and Diversity of Putative Aminoglycoside-Biosynthetic Aminotransferase Genes from Deep-Sea Environmental DNA

“…[7][8][9][10][11] The gene stsC encodes aminotransferase involved in the biosynthetic pathway of streptomycin. 7) This enzyme catalyzes the transfer of an amino group from Lglutamine to scyllo-inosose, and contributes to the biosynthesis of aglycone in streptomycin. Subsequently, L-glutamine:2-deoxy-scyllo-inosose aminotransferase (BtrS) was identified in the butirosin-producer Bacillus circulans.…”

“…However, it is unlikely that this replacement affects the enzyme activity, because the activity of StsC has been confirmed. 7) Additionally, the corresponding residue in SpcE is Gln. The substrate specificity of SpcE should be the same as that of StsC, because SpcE is involved in the biosynthesis of spectinomycin, which contains the same aglycone (fully-substituted aminocyclitol) with streptomycin.…”

Identification of Aminotransferase Genes for Biosynthesis of Aminoglycoside Antibiotics from Soil DNA

“…Genetic and enzymological studies have been performed for the biosynthesis of these antibiotics. [12][13][14] The other group of aminoglycosides has a common aglycone of 2-deoxystreptamine (DOS), and clinically important and major compounds are included in this category, such as neomycin, kanamycin, ribostamycin, butirosin, gentamicin, tobramycin, sisomicin, sagamicin, etc. Genetic and biochemical studies of these compounds have not succeeded lately.…”