Metamorphic enzyme assembly in polyketide diversification

Natural product chemical diversity is fuelled by the emergence and ongoing evolution of biosynthetic pathways in secondary metabolism. However, co-evolution of enzymes for metabolic diversification is not well understood, especially at the biochemical level. Here, two parallel assemblies with an extraordinarily high sequence identity from Lyngbya majuscula form a Β-branched cyclopropane in the curacin A pathway (Cur), and a vinyl chloride group in the jamaicamide pathway (Jam). The components include a halogenase, a 3-hydroxy-3-methylglutaryl enzyme cassette for polyketide Β-branching, and an enoyl reductase domain. The halogenase from CurA, and the dehydratases (ECH"1s), decarboxylases (ECH"2s) and enoyl reductase domains from both Cur and Jam, were assessed biochemically to determine the mechanisms of cyclopropane and vinyl chloride formation. Unexpectedly, the polyketide Β-branching pathway was modified by introduction of a -chlorination step on (S)-3-hydroxy-3-methylglutaryl mediated by Cur halogenase, a non-haem Fe(ii), α-ketoglutarate-dependent enzyme. In a divergent scheme, Cur ECH"2 was found to catalyse formation of the α,Β enoyl thioester, whereas Jam ECH"2 formed a vinyl chloride moiety by selectively generating the corresponding Β, enoyl thioester of the 3-methyl-4-chloroglutaconyl decarboxylation product. Finally, the enoyl reductase domain of CurF specifically catalysed an unprecedented cyclopropanation on the chlorinated product of Cur ECH"2 instead of the canonical α,Β C ≤ C saturation reaction. Thus, the combination of chlorination and polyketide Β-branching, coupled with mechanistic diversification of ECH"2 and enoyl reductase, leads to the formation of cyclopropane and vinyl chloride moieties. These results reveal a parallel interplay of evolutionary events in multienzyme systems leading to functional group diversity in secondary metabolites. © 2009 Macmillan Publishers Limited. All rights reserved

Progress challenges and opportunities for the re-engineering of trans-AT polyketide synthases

Polyketides are a structurally and functionally diverse family of bioactive natural products that are used extensively as pharmaceuticals and agrochemicals. In bacteria these molecules are biosynthesized by giant, multi-functional enzymatic complexes, termed modular polyketide synthases (PKSs), that function in assembly-line like fashion to fuse and tailor simple carboxylic acid monomers into a vast array of elaborate chemical scaffolds. Modifying PKSs through targeted synthase re-engineering is a promising approach for accessing functionally-optimized polyketides. Due to their highly mosaic architectures the recently identified trans-AT family of modular synthases appear inherently more amenable to re-engineering than their well studied cis-AT counterparts. Here, we review recent progress in the re-engineering of trans-AT PKSs, summarize opportunities for harnessing the biosynthetic potential of these systems, and highlight challenges that such re-engineering approaches present. </p

Alleviation of Abiotic and Biotic Stresses in Plants by Azospirillum

International audienc

Microbial-Assisted Phytoremediation: A Convenient Use of Plant and Microbes to Clean Up Soils

Environmental pollution by metal(loid)s (e.g., heavy metals—HMs) is a severe problem worldwide, as soils and aquatic resources became increasingly contaminated, threatening land ecosystems, surface and groundwater, as well as food safety and human health. The primary sources contributing to this extended pollution are anthropogenic inputs related to the burning of fossil fuels, mining and continued industrial activities, disposal of municipal solid wastes and wastewater discharges or use for irrigation, and excessive utilization of fertilizers and pesticides. A consequence of these anthropogenic activities is an increase of contaminated areas, which should be remediated to prevent or mitigate transfer of contaminants into terrestrial, atmospheric, or aquatic environments. Point and diffuse contamination by organic and inorganic pollutants causes wide concerns, and intentional or accidental introduction of these substances in the environment may represent serious impacts on public health