Polyketides are a group of natural products with valuable pharmacological activities, biosynthesized by bacterial or fungal megaenzymes called polyketide synthases (PKSs). These are composed of multiple modules in an assembly line, each introducing a specific moiety of the final compound in a stepwise manner. Among them, trans-acyltransferase PKSs have evolved through the recombination of biosynthetic gene clusters. Now, Mabesoone et al. report in Science the identification, by coevolution analysis, of a common amino acid motif for hybrid PKS formation. This motif — LPTYPF(X5)W — is found to be a boundary between the ketosynthase domain and a C-terminal region that yields functional PKSs upon trans-acyltransferase PKS recombination. The team used it as an artificial fusion site in the oocydin biosynthetic gene cluster: only LPTYPF(X5)W-fused chimeras could produce the desired chlorinated compounds. Fusion of the motif to a range of different exchange units also enabled the biosynthesis in diverse bacterial hosts of elongated, varied substrates active against HeLa cells.

On a similar topic, Bozhüyük et al., also in Science, report the use of computational modelling and principal component analyses to understand the intragenomic recombination of nonribosomal peptide synthetases (NRPSs). They identified regions that do not share consistent phylogenetic histories as synthetic breakpoints for engineering NRPSs with high success rates. NRPSs are molecular assembly lines composed of several repeating modules of catalytic domains that biosynthesize complex peptides independently of ribosomes. The team’s approach, termed ‘exchange unit between T domains’ (XUT), allowed the identification of the conserved FFXXGGXS amino acid motif as a recombination site in the thiolation domain. Its application enabled the obtainment of recombinant NRPSs that produced biologically active peptides against the eukaryotic proteasome.