Characterization of the flavin monooxygenase involved in biosynthesis of the antimalarial FR-900098.

The latter steps in this biosynthetic pathway for the antimalarial phosphonic acid FR-900098 include the installation of a hydroxamate onto 3-aminopropylphosphonate, which is catalyzed by the consecutive actions of an acetyltransferase and an amine hydroxylase. Here, we present the 1.6 Å resolution co-crystal structure and accompanying biochemical characterization of FrbG, which catalyzes the hydroxylation of aminopropylphosphonate. We show that FrbG is a flavin-dependent N-hydroxylating monooxygenase (NMO), which shares a similar overall structure with flavin-containing monooxygenases (FMOs). Notably, we also show that the cytidine-5'-monophosphate moiety of the substrate is a critical determinant of specificity, distinguishing FrbG from other FMOs in that the nucleotide cofactor-binding domain also serves in conferring substrate recognition. In the FrbG-FAD+-NADPH co-crystal structure, the C4 of the NADPH nicotinamide is situated near the N5 of the FAD isoalloxazine, and is oriented with a distance and stereochemistry to facilitate hydride transfer.

Structure-guided design and biosynthesis of a novel FR-900098 analogue as a potent Plasmodium falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr) inhibitor.

We report here the enzymatic biosynthesis of FR-900098 analogues and establish an in vivo platform for the biosynthesis of an N-propionyl derivative FR-900098P. FR-900098P is found to be a significantly more potent inhibitor of Plasmodium falciparum 1-deoxy-D-xylulose 5-phosphate reductoisomerase (PfDxr) than the parent compound, and thus a more promising antimalarial drug candidate.

New N-acetyltransferase fold in the structure and mechanism of the phosphonate biosynthetic enzyme FrbF.

The enzyme FrbF from Streptomyces rubellomurinus has attracted significant attention due to its role in the biosynthesis of the antimalarial phosphonate FR-900098. The enzyme catalyzes acetyl transfer onto the hydroxamate of the FR-900098 precursors cytidine 5'-monophosphate-3-aminopropylphosphonate and cytidine 5'-monophosphate-N-hydroxy-3-aminopropylphosphonate. Despite the established function as a bona fide N-acetyltransferase, FrbF shows no sequence similarity to any member of the GCN5-like N-acetyltransferase (GNAT) superfamily. Here, we present the 2.0 Å resolution crystal structure of FrbF in complex with acetyl-CoA, which demonstrates a unique architecture that is distinct from those of canonical GNAT-like acetyltransferases. We also utilized the co-crystal structure to guide structure-function studies that identified the roles of putative active site residues in the acetyltransferase mechanism. The combined biochemical and structural analyses of FrbF provide insights into this previously uncharacterized family of N-acetyltransferases and also provide a molecular framework toward the production of novel N-acyl derivatives of FR-900098.

Characterization and application of the Fe(II) and α-ketoglutarate dependent hydroxylase FrbJ.

The Fe(II) and α-ketoglutarate-dependent hydroxylase FrbJ was previously demonstrated to utilize FR-900098 synthesizing a second phosphonate FR-33289. Here we assessed its ability to hydroxylate other possible substrates, generating a library of potential antimalarial compounds. Through a series of bioassays and in vitro experiments, we identified two new antimalarials.

Deciphering the late biosynthetic steps of antimalarial compound FR-900098.

FR-900098 is a potent chemotherapeutic agent for the treatment of malaria. Here we report the heterologous production of this compound in Escherichia coli by reconstructing the entire biosynthetic pathway using a three-plasmid system. Based on this system, whole-cell feeding assays in combination with in vitro enzymatic activity assays reveal an unusual functional role of nucleotide conjugation and lead to the complete elucidation of the previously unassigned late biosynthetic steps. These studies also suggest a biosynthetic route to a second phosphonate antibiotic, FR-33289. A thorough understanding of the FR-900098 biosynthetic pathway now opens possibilities for metabolic engineering in E. coli to increase production of the antimalarial antibiotic and combinatorial biosynthesis to generate novel derivatives of FR-900098.