# Evolutionary Reprogramming of Acyltransferase Domains in Polyene Macrolide Pathways

## TL;DR

This study explores how acyltransferase domains in polyketide pathways evolved and can be reprogrammed to create new antibiotic compounds.

## Contribution

The paper reveals a novel mechanism of acyltransferase functional reprogramming and applies it to engineer new polyketide antibiotics.

## Key findings

- A eurocidin biosynthetic pathway was identified with divergent loading module architectures.
- AT domains were reprogrammed to shift substrate specificity from extender to starter units.
- Engineering the candicidin pathway produced aliphatic-starting analogs using the reprogrammed AT domains.

## Abstract

The evolution of type I polyketide synthase (T1PKS) assembly lines remains poorly understood. Through systematic mining of polyene biosynthetic gene clusters, we identified a novel eurocidin biosynthetic pathway capable of producing identical compounds with divergent loading module architectures, thereby capturing an evolutionary transitional state. Biochemical analysis revealed unprecedented functional reprogramming of acyltransferase (AT) domains, shifting substrate specificity from extender units (malonyl-CoA) to starter units (acyl-CoA). This paradigm shift enables direct initiation of polyketide chain assembly via AT-mediated loading of starter units, thereby elucidating the origin of extant AT-initiated assembly lines and establishing AT functional plasticity as a novel mechanism for polyketide structural diversification. Parallel evolution of ketosynthase (KS) domains through KSS→KSQ mutations further diversified initiation strategies. Applying this evolutionary insight, we engineered the candicidin pathway by replacing its native aromatic-starting bimodule with a starter-selective monomodule from eurocidin, generating aliphatic-starting analogs. This demonstrates that evolution-inspired AT reprogramming provides a rational framework for modifying polyketide starter units, expanding structural diversity, and enhancing therapeutic potential.