A Branch Point of Streptomyces Sulfur Amino Acid Metabolism Controls the Production of Albomycin

Abstract

c Albomycin (ABM), also known as grisein, is a sulfur-containing metabolite produced by Streptomyces griseus ATCC 700974. Genes predicted to be involved in the biosynthesis of ABM and ABM-like molecules are found in the genomes of other actinomycetes. ABM has potent antibacterial activity, and as a result, many attempts have been made to develop ABM into a drug since the last century. Although the productivity of S. griseus can be increased with random mutagenesis methods, understanding of Streptomyces sulfur amino acid (SAA) metabolism, which supplies a precursor for ABM biosynthesis, could lead to improved and stable production. We previously characterized the gene cluster (abm) in the genome-sequenced S. griseus strain and proposed that the sulfur atom of ABM is derived from either cysteine (Cys) or homocysteine (Hcy). The gene product, AbmD, appears to be an important link between primary and secondary sulfur metabolic pathways. Here, we show that propargylglycine or iron supplementation in growth media increased ABM production by significantly changing the relative concentrations of intracellular Cys and Hcy. An SAA metabolic network of S. griseus was constructed. Pathways toward increasing Hcy were shown to positively impact ABM production. The abmD gene and five genes that increased the Hcy/Cys ratio were assembled downstream of hrdBp promoter sequences and integrated into the chromosome for overexpression. The ABM titer of one engineered strain, SCAK3, in a chemically defined medium was consistently improved to levels ϳ400% of the wild type. Finally, we analyzed the production and growth of SCAK3 in shake flasks for further process development. The Streptomyces genus was established at the beginning of the golden age of antibiotic discovery (1). Streptomyces griseus, a representative organism of the genus (2), was shown during this time to produce streptomycin (3), which has been clinically used to treat bacterial infections and other human diseases. It is well known that Streptomyces organisms in general have a large biosynthetic potential, being capable of producing many bioactive secondary metabolites-the S. griseus strains producing albomycin (ABM) are no exception. ABM was named by former Soviet Union scientists and underwent clinical investigations well before the information was released to the English-speaking scientific world (4). The biological activity and chemical constitution of ABM were later reported to be nearly identical to those of grisein, which was isolated from a distinct subtype of S. griseus by U.S. scientists in the 1940s (5-7). Despite its remarkable properties, continued studies of ABM were not pursued, partly because of the poor yields (8) and unpublicized research on the microorganism (9, 10). At present, the wealth of Streptomyces genomic information that is publically available provides the possibility of using a systems biology approach to uncover new aspects of Streptomyces metabolism and potentially overcome the production bottleneck.ABM and ABM-like secondary metabolites...

Discovering the potential of S. clavuligerus for bioactive compound production: cross-talk between the chromosome and the pSCL4 megaplasmid

“…Also, the cystathionine-γ-lyase ( cysA ) contributes to cysteine formation (Additional file 1: Figure S5B). However, the genes SCLAV_5668, encoding a cystathionine-γ-synthase, and SCLAV_p1477, encoding a cysteine synthase, do not exist in S. clavuligerus pSCL4-; in addition, a gene homologous to metC, for a cystathionine β-lyase [ 35 ] has not been detected in S. clavuligerus genome . Sulfur metabolism in Streptomyces is still poorly understood, and more biochemical studies are required to know relationship between genes and enzymes and regulatory mechanisms in Streptomyces cysteine-methionine metabolism.…”

Total synthesis and antimicrobial evaluation of natural albomycins against clinical pathogens

“…Surprisingly, a single replacement of the sulfur with oxygen resulted in the complete loss of antibacterial activity, suggesting a critical role of the sulfur atom in the activity of albomycins. A biosynthetic approach has also been attempted for the generation of albomycin analogs 23 , but albomycin production by S. griseus is difficult and has yet to be scaled up efficiently 24 . Herein, we describe the total synthesis of the three natural albomycins ( 1a – c ), which features a Pummerer reaction for nucleobase introduction and an aldol reaction to expand the side chain of thionucleoside.…”

Biosynthetic Origin of the Atypical Stereochemistry in the Thioheptose Core of Albomycin Nucleoside Antibiotics

“…13 The gene abmD in the abm gene cluster encodes another PLP-dependent enzyme, although it does not show high sequence similarity to known racemases/epimerases. While it has been reported that overexpression of abmD increases the level of 1 production, 14 the catalytic role of the gene product AbmD has not been characterized. To determine whether AbmD can catalyze the epimerization of the AbmH-product 28 (or its physiological equivalent), N -His 6 -tagged AbmD was heterologously overexpressed and purified from E. coli (Figure S2).…”