Investigating amine derivatives of ambruticin VS-5 and VS-4.

A structure-activity relationship around the amine group of the ambruticin VS series has been developed for antifungal activity. It was shown that the amine can be alkylated through reductive amination without loss of potency. However, if it is converted into either an amide, carbamate, or urea, a significant loss of potency is observed. Of the alkyl amines, small nonpolar groups are optimal for both potency and oral bioavailability. As a result of this study, one compound (KOS-2079) was taken into an animal efficacy model with success.

Characterization of the heterodimeric MegBIIa:MegBIIb aldo-keto reductase involved in the biosynthesis of L-mycarose from Micromonospora megalomicea.

Two putative C3-ketoreductases, MegBIIa and MegBIIb (formerly MegBII and MegDVII, respectively), homologues to members of the family 12 of aldo-keto reductase (AKR12) superfamily of enzymes, were identified in the megalomicin gene cluster from Micromonospora megalomicea. Proteins from this family are involved in the metabolism of TDP-sugars by actinomycetes. MegBIIa was originally proposed to be involved in the l-mycarose biosynthetic pathway, while MegBIIb in the l-megosamine biosynthetic pathway. In this work we have investigated the role of these proteins in the biosynthesis of dTDP-l-mycarose. In vivo analysis of the dTDP-sugar intermediates indicated that neither MegBIIa nor its homologue, MegBIIb, was a fully active enzyme by itself. Surprisingly, C3-ketoreductase activity was observed only in the presence of both MegBIIa and MegBIIb, suggesting the formation of an active complex. Copurification and size exclusion chromatography experiments confirmed that MegBIIa and MegBIIb interact forming a 1:1 heterodimeric complex. Finally, a mycarose operon containing megBIIa and megBIIb together with the other biosynthetic genes of the l-mycarose pathway was constructed and tested by bioconversion experiments in Escherichia coli. High levels of mycarosyl-erythronolide B were produced under the condition tested, confirming the role of these two proteins in this metabolic pathway.

Redesign, synthesis and functional expression of the 6-deoxyerythronolide B polyketide synthase gene cluster.

A generic design of Type I polyketide synthase genes has been reported in which modules, and domains within modules, are flanked by sets of unique restriction sites that are repeated in every module [1]. Using the universal design, we synthesized the six-module DEBS gene cluster optimized for codon usage in E. coli, and cloned the three open reading frames into three compatible expression vectors. With one correctable exception, the amino acid substitutions required for restriction site placements were compatible with polyketide production. When expressed in E. coli the codon-optimized synthetic gene cluster produced significantly more protein than did the wild-type sequence. Indeed, for optimal polyketide production, PKS expression had to be down-regulated by promoter attenuation to achieve balance with expression of the accessory proteins needed to support polyketide biosynthesis.