Effect of phosphate and amino acids on echinomycin biosynthesis by Streptomyces echinatus

Abstract

Streptomyces echinatus produces only echinomycin (quinomycin A), in contrast to other streptomycetes, which produce families of quinoxaline antibiotics differing in the amino acid composition of the oligopeptide (quinomycins A, B, Bo, C, D, and E) or the structure of the sulfur-containing cross bridge (triostins A, B, and C). Attempts were made to establish conditions for directed biosynthesis with S. echinatus. The lability of the peptide lactone to alkaline pH was obviated by using high levels of phosphate or HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] buffer in the production medium. Maintaining the pH below 7.5 resulted in an apparent stimulation of production. Amino acids which serve as structural components or as precursors of echinomycin were employed singly or in combination with nitrate in a chemically defined medium. Based on specific yield (micrograms of echinomycin per milligram of mycelia [dry weight]), D-and L-serine, D-alanine, L-valine, and L-phenylalanine produced equivalent yields of antibiotic which were approximately twofold greater than yields obtained with nitrate alone. In contrast, L-alanine, P-alanine, and L-threonine produced a threeto fourfold stimulation of production. Although the other amino acids diminished antibiotic production, L-isoleucine, which ostensibly was inhibitory to production, supported the accumulation of a quinoxaline antibiotic in which the crossbridge sulfur lacked a methyl group.The family of quinoxaline antibiotics embraces two structurally related series referred to as the triostins and the quinomycins. Both series are similar in composition, consisting of two quinoxaline-2-carboxylic acid moieties attached to a cyclic octapeptide which contains a sulfur cross-linkage. They are distinguished in that the triostins contain a disulfide cross bridge, whereas the quinomycins contain a thioacetal cross bridge (3). The circularity of the oligopeptide is maintained by lactone bonds between the hydroxyl group of D-serine and the carboxyl group of the N-methyl amino acid (Fig. 1).Echinomycin (quinomycin A) differs from other natural quinomycin congeners in that its oligopeptide contains 2 mol each of N-methyl-Lvaline, D-serine, L-alanine, and L-cysteine (the latter as N-methyl-L-cysteine and N-methyl-Smethyl cysteine) (11). The major difference among the other natural congeners resides in the N-methyl amino acid residue which can occur as mono-or dimethylated alloisoleucines (11,15,18) with or without N-methyl valine in the other half-molecule.

Echinomycin, a Small-Molecule Inhibitor of Hypoxia-Inducible Factor-1 DNA-Binding Activity

“…NSC-13502, a cyclic peptide of the family of quinoxaline antibiotics that was originally isolated from Streptomyces echinatus (45), is a small molecule known to bind DNA in a sequence-specific fashion. The strong binding sites for NSC-13502 contain the central 2-bp sequence 5V-CG-3V, and the key recognition elements for NSC-13502 are contained in the sequences 5V-ACGT-3V and 5V-TCGT-3V (15).…”

Hypoxia Inducible Factor Pathway Inhibitors as Anticancer Therapeutics

“…Echinomycin (quinomycin A, NSC 526417) is a cyclic peptide antibiotic agent of quinoxaline that was originally isolated from Streptomyces echinatus [168]. Echinomycin is known to bind DNA in a sequence-specific manner.…”

Negative Regulation of Human Growth Hormone Gene Expression by Insulin Is Dependent on Hypoxia-inducible Factor Binding in Primary Non-tumor Pituitary Cells

“…Echinomycin is a cyclic peptide, antibiotic, and specific DNA binding factor with a strong affinity for the 5Ј-ACGTG-3Ј sequence, which is at the core of a HBS (46,47). Cultures were incubated with 10 nM echinomycin 1 h before insulin treatment.…”