Streptothricin biosynthesis is catalyzed by enzymes related to nonribosomal peptide bond formation

Abstract

In a search for strains producing biocides with a wide spectrum of activity, a new strain was isolated. This strain was taxonomically characterized as Streptomyces rochei F20, and the chemical structure of the bioactive product extracted from its fermentation broth was determined to be a mixture of streptothricins. From a genomic library of the producer strain prepared in the heterologous host Streptomyces lividans, a 7.2-kb DNA fragment which conferred resistance to the antibiotic was isolated. DNA sequencing of 5.2 kb from the cloned fragment revealed five open reading frames (ORFs) such that ORF1, -2, -3, and -4 were transcribed in the same direction while ORF5 was convergently arranged. The deduced product of ORF1 strongly resembled those of genes involved in peptide formation by a nonribosomal mechanism; the ORF2 product strongly resembled that of mphA and mphB isolated from Escherichia coli, which determines resistance to several macrolides by a macrolide 2-phosphotransferase activity; the ORF3 product had similarities with several hydrolases; and the ORF5 product strongly resembled streptothricin acetyltransferases from different gram-positive and gramnegative bacteria. ORF5 was shown to be responsible for acetyl coenzyme A-dependent streptothricin acetylation. No similarities in the databases for the ORF4 product were found. Unlike other peptide synthases, that for streptothricin biosynthesis was arranged as a multienzymatic system rather than a multifunctional protein.Insertional inactivation of ORF1 and ORF2 (and to a lesser degree, of ORF3) abolishes antibiotic biosynthesis, suggesting their involvement in the streptothricin biosynthetic pathway.During a screening process, a streptomycete producer of broad-range antibiotic activity was isolated from soil samples; this strain has been taxonomically characterized as Streptomyces rochei F20, and its active compound has been described as a mixture of streptothricins (mostly F and traces of D and E) (41a). The present paper describes the isolation, DNA sequence, and partial characterization of the biosynthetic pathway for streptothricin produced by this newly isolated strain. Streptothricin was one of the first actinomycete antibiotics to be described (56). It has a broad spectrum, with antibacterial as well as antifungal activity. Its chemical elucidation was described by Kusumoto and coworkers (30) (Fig. 1). It contains a heterocyclic ␤-amino acid (streptolidine), an amino sugar (4-carbamido-D-gulosamine), and, by amide linkage at C-2, a ␤-lysine chain which varies from one to six units in streptothricins F to A, respectively, and which includes seven units for streptothricin X (22, 31). More recently, other members of the family, which are chemically closely related to streptothricin, have been described (1,23,25).Members of the streptothricin family have, in addition to a potent inhibitory activity for prokaryotic protein synthesis (11), cytotoxicity which prevents their clinical or veterinary use. However, this may well be useful in situations in wh...

Identification of the biosynthetic gene cluster of A-500359s in Streptomyces griseus SANK60196

“…To date, six complete biosynthetic gene clusters for nucleoside antibiotics have been cloned and reported: nikkomycin and polyoxin, peptidyl nucleoside antibiotics containing a uracil-or 4-formyl-imidazolin-2-one base; 5,6 puromycin, an adeninecontaining aminonucleoside antibiotic; 7 streptothricins, peptidyl guanidine nucleoside antibiotics; 8 and blasticidin S 9 and toyocamycin, pyrrolopyrimidine nucleoside antibiotics. 10 Furthermore, two enzymes involved in mildiomycin biosynthesis have been functionally characterized.…”

Inhibition of Epsilon-Poly- l -Lysine Biosynthesis in Streptomycetaceae Bacteria by Short-Chain Polyols

“…Currently, only the biosynthesis of the poly-␤-lysine chain of streptothricin fits under this classification, although this peptide is not free but is associated with a D-gulosamine core. The gene encoding the ␤-lysine-adenylating enzyme involved in poly-␤-lysine chain assembly is well characterized (4,6). The deduced amino acid sequence exhibits homology with other NRPS family members.…”

A Novel Enzyme Conferring Streptothricin Resistance Alters the Toxicity of Streptothricin D from Broad-spectrum to Bacteria-specific

“…Strains-Based on the highly conserved amino acid sequence of the NATs of S. lavendulae (16), S. rochei (17), and S. noursei (18,19), we designed primers 5Ј-…”

“…1). In fact, in ST producers such as S. lavendulae (16), Streptomyces rochei (17), and Streptomyces noursei (18,19), the ST-resistance genes encoding N-acetyltransferase (NAT) have been identified and their role in selfresistance against their own STs has been investigated. Based on this resistance mechanism and the fact that streptothricin D (ST-D) is a more effective antibiotic than streptothricin F (ST-F), the moiety of ␤-lysine(s) has been shown to play a crucial role in antibiotic activity.…”