The StrQ protein encoded in the gene cluster for 5'-hydroxystreptomycin of Streptomyces glaucescens GLA.0 is a alpha-D-glucose-1-phosphate cytidylyltransferase (CDP-D-glucose synthase).
The gene strQ was identified as the last gene of a putative transcription unit, strB1FGHPQ, located in the gene cluster for the production of 5'-hydroxy-streptomycin (OH-Sm) in Streptomyces glaucescens GLA.0. [In contrast, the corresponding operon in the str/sts-gene cluster of the Sm-producer Streptomyces griseus, strB1FGHIK, differs in the two distal genes; Mansouri, K. & Piepersberg, W. (1991) Mol. Gen. Genet. 228, 459-469]. The deduced StrQ protein exhibited similarities to members of the enzyme family of hexose-1-phosphate nucleotidylyltransferases (NDP-hexose synthases or pyrophosphorylases), with the strongest similarity to the subfamily of alpha-D-glucose-1-phosphate cytidylyltransferases (CDP-D-glucose synthases). The StrQ protein was heterologously expressed in Escherichia coli. The purified protein revealed an enzyme activity of that of a CDP-D-glucose synthase and a substrate specificity restricted to CTP and alpha-D-glucose 1-phosphate. The K(m) and Vmax values determined for CTP are 44 microM and 920 microM and for alpha-D-glucose 1-phosphate 195 microM and 1.06 mM, respectively. The CDP-D-glucose synthase activity was also detected in cells of S. glaucescens under the conditions of antibiotic production, but was absent from cells of the streptomycin producer S. griseus N2-3-11. Also, the genomes of several strains of S. griseus did not seem to possess strQ-related genes. In contrast, hybridisation experiments indicated that genes homologous to strQ were probably present in various other actinomycetes producing aminoglycosides. A possible function of the StrQ protein in the OH-Sm biosynthetic pathway of GLA.0 is discussed.
Beyer
S
S
Bergische Universität GH Wuppertal, Germany.
Mayer
G
G
Piepersberg
W
W
D000595:Amino Acid Sequence; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D007700:Kinetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D009713:Nucleotidyltransferases / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D009876:Operon; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification; D012155:Reticulin / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics*; D013379:Substrate Specificity