No abstract

Apramycin is aclinically promising aminoglycoside antibiotic (AGA). To date,m echanisms underlying the biosynthesis and self-resistance of apramycin remain largely unknown. Here we report that apramycin biosynthesis proceeds through unexpected phosphorylation, deacetylation, and dephosphorylation steps,i nw hich an ovel aminoglycoside phosphotransferase (AprU), ap utative creatinine amidohydrolase (AprP), and an alkaline phosphatase (AprZ) are involved. Biochemical characterization revealed that AprU specifically phosphorylates 5-OH of ap seudotrisaccharide intermediate,w hose N-7' acetyl group is subsequently hydrolyzed by AprP.A prZ is located extracellularly where it removes the phosphate group from ap seudotetrasaccharide intermediate,leading to the maturation of apramycin. Intriguingly,7'-N-acetylated and 5-O-phosphorylated apramycin that were accumulated in DaprU and DaprZ respectively exhibited significantly reduced antibacterial activities,i mplying Streptomyces tenebrarius employs C-5 phosphorylation and N-7' acetylation as two strategies to avoid auto-toxicity.S ignificantly,t his study provides insight into the design of new generation AGAs to circumvent the emergence of drugresistant pathogens.

β-Hydroxy-α-amino acids (βH-AAs) are key components of many bioactive molecules as well as exist as specialised metabolites. Among these βH-AAs, 4-fluorothreonine (4-FT) is the only naturally occurring fluorinated AA discovered thus far. Here we report overexpression and biochemical characterisation of 4-fluorothreonine transaldolase from Streptomyces sp. MA37 (FTaseMA), a homologue of FTase previously identified in the biosynthesis of 4-FT in S. cattleya. FTaseMA displays considerable substrate plasticity to generate 4-FT as well as other β-hydroxy-α-amino acids with various functionalities at C4 position, giving the prospect of new chemo-enzymatic applications. The enzyme has a hybrid of two catalytic domains, serine hydroxymethyltransferase (S) and aldolase (A). Site-directed mutagenesis allowed the identification of the key residues of FTases, suggesting that the active site of A domain has a historical reminiscent feature in metal-dependent aldolases. Elemental analysis demonstrated that FTaseMA is indeed a Zn 2+ -dependent enzyme, the first example of pyridoxal phosphate (PLP) enzyme family fused with a metal-binding domain carrying out a distinct catalytic role. Finally, FTaseMA showed divergent evolutionary origin with other PLP dependent enzymes.

Streptomyces remains one of the prolific sources of structural diversity, and a reservoir to mine for novel natural products. Continued screening for new Streptomyces strains in our laboratory led to the isolation of Streptomyces sp. RK44 from the underexplored areas of Kintampo waterfalls, Ghana, Africa. Preliminary screening of the metabolites from this strain resulted in the characterization of a new 2-alkyl-4-hydroxymethylfuran carboxamide (AHFA) 1 together with five known compounds, cyclo-(L-Pro-Gly) 2, cyclo-(L-Pro-L-Phe) 3, cyclo-(L-Pro-L-Val) 4, cyclo-(L-Leu-Hyp) 5, and deferoxamine E 6. AHFA 1, a methylenomycin (MMF) homolog, exhibited anti-proliferative activity (EC50 = 89.6 µM) against melanoma A2058 cell lines. This activity, albeit weak is the first report amongst MMFs. Furthermore, the putative biosynthetic gene cluster (ahfa) was identified for the biosynthesis of AHFA 1. DFO-E 6 displayed potent anti-plasmodial activity (IC50 = 1.08 µM) against P. falciparum 3D7. High-resolution electrospray ionization mass spectrometry (HR ESIMS) and molecular network assisted the targeted-isolation process, and tentatively identified six AHFA analogues, 7–12 and six siderophores 13–18.

Apramycin is aclinically promising aminoglycoside antibiotic (AGA). To date,m echanisms underlying the biosynthesis and self-resistance of apramycin remain largely unknown. Here we report that apramycin biosynthesis proceeds through unexpected phosphorylation, deacetylation, and dephosphorylation steps,i nw hich an ovel aminoglycoside phosphotransferase (AprU), ap utative creatinine amidohydrolase (AprP), and an alkaline phosphatase (AprZ) are involved. Biochemical characterization revealed that AprU specifically phosphorylates 5-OH of ap seudotrisaccharide intermediate,w hose N-7' acetyl group is subsequently hydrolyzed by AprP.A prZ is located extracellularly where it removes the phosphate group from ap seudotetrasaccharide intermediate,leading to the maturation of apramycin. Intriguingly,7'-N-acetylated and 5-O-phosphorylated apramycin that were accumulated in DaprU and DaprZ respectively exhibited significantly reduced antibacterial activities,i mplying Streptomyces tenebrarius employs C-5 phosphorylation and N-7' acetylation as two strategies to avoid auto-toxicity.S ignificantly,t his study provides insight into the design of new generation AGAs to circumvent the emergence of drugresistant pathogens.