Generation of reduced macrolide analogs by regio-specific biotransformation

Engineering actinomycetes for biosynthesis of macrolactone polyketides

Actinobacteria are characterized as the most prominent producer of natural products (NPs) with pharmaceutical importance. The production of NPs from these actinobacteria is associated with particular biosynthetic gene clusters (BGCs) in these microorganisms. The majority of these BGCs include polyketide synthase (PKS) or non-ribosomal peptide synthase (NRPS) or a combination of both PKS and NRPS. Macrolides compounds contain a core macro-lactone ring (aglycone) decorated with diverse functional groups in their chemical structures. The aglycon is generated by megaenzyme polyketide synthases (PKSs) from diverse acyl-CoA as precursor substrates. Further, post-PKS enzymes are responsible for allocating the structural diversity and functional characteristics for their biological activities. Macrolides are biologically important for their uses in therapeutics as antibiotics, anti-tumor agents, immunosuppressants, anti-parasites and many more. Thus, precise genetic/metabolic engineering of actinobacteria along with the application of various chemical/biological approaches have made it plausible for production of macrolides in industrial scale or generation of their novel derivatives with more effective biological properties. In this review, we have discussed versatile approaches for generating a wide range of macrolide structures by engineering the PKS and post-PKS cascades at either enzyme or cellular level in actinobacteria species, either the native or heterologous producer strains.

Regio-selectively reduced streptogramin A analogue, 5,6-dihydrovirginiamycin M1 exhibits improved potency against MRSA

A newly reduced macrocyclic lactone antibiotic streptogramin A, 5,6-dihydrovirginiamycin M1 was created by feeding virginiamycin M1 into a culture of recombinant Streptomyces venezuelae. Its chemical structure was spectroscopically elucidated, and this streptogramin A analogue showed twofold higher antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) compared with its parent molecule virginiamycin M1. Docking studies using the model of streptogramin A acetyltransferase (VatA) suggested that the newly generated analogue binds tighter with overall lower free energy compared with the parent molecule virginiamycin M1. This hypothesis was validated experimentally through the improvement of efficacy of the new analogue against MRSA strains. The biotransformation approach presented herein could have a broad application in the production of reduced macrocyclic molecules.