Engineering actinomycetes for biosynthesis of macrolactone polyketides

Abstract

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.

Keywords: Actinomycetes; Biosynthesis; Biosynthetic gene clusters; Macrolides; Metabolic engineering; Polyketide synthase.

Fig. 1

Structures of different macrocyclic compounds with their primary producer strain and potential use of these molecules

Fig. 2

Biosynthetic gene assembly of tylosin biosynthesis gene cluster illustrating condensation and modification of different extender units to form tylactone aglycone which is further decorated with different post-modification enzymes to form tylosin

Fig. 3

Structure of tylosin showing possible modification/engineering sites for engineering/diversification of tylosin and related molecules

Fig. 4

a Biosynthesis pathway assembly of erythromycin. b Biosynthesis of diverse erythromycin derivatives using Streptomyces coelicolor deficient in KS1⁰. Different activated synthetic diketides and triketides were supplemented to the culture

Fig. 5

Structures of different sugars conjugated macrolides produced using TDP-sugars biosynthesis pathway engineered Streptomyces recombinant strains

Fig. 6

Generation of different macrolactones using selected enzymes such as PikC, EryF and OleP

Fig. 7

Biosynthesis of benzyoyl erythromycin by replacing loading module of erythromycin from loading module of rifamycin biosynthesis pathway

Fig. 8

Chemoenzymatic and biocatalytic synthesis of structurally diverse tylactone-based macrolides antibiotics

Fig. 9

a Biosynthesis of glycosylated macrolides from different TDP-sugars (TDP-L-mycarose, TDP-desosamine, TDP-megosamine) biosynthesis pathway overexpressed recombinant E. coli strains supplemented with corresponding macrolactone/macrolides. b Biotransformation of macrolides using Streptomyces venezuelae strain

Fig. 9

a Biosynthesis of glycosylated macrolides from different TDP-sugars (TDP-L-mycarose, TDP-desosamine, TDP-megosamine) biosynthesis pathway overexpressed recombinant E. coli strains supplemented with corresponding macrolactone/macrolides. b Biotransformation of macrolides using Streptomyces venezuelae strain