Engineering an Extremely Hybrid PKS for Adipic Acid Production

Area of Science:

• Biochemistry
• Synthetic Biology
• Metabolic Engineering

Background:

• Polyketide synthases (PKSs) are versatile modular enzymes.
• PKSs are valuable biocatalysts for producing non-native compounds.
• Adipic acid (AA) is an important industrial monomer for nylon production.

Purpose of the Study:

• To engineer the first PKS-based pathway for adipic acid (AA) production.
• To develop a novel biocatalytic route for AA synthesis.
• To expand the PKS toolkit for producing dicarboxylic acids.

Main Methods:

• Retrosynthetic analysis to identify key PKS modules.
• Engineering a succinyl-CoA-loading module (EtnB) that retains the terminal carboxyl group.
• Constructing a highly chimeric PKS by integrating domains from multiple organisms.
• Functional expression in *Escherichia coli* and *Pseudomonas putida*.
• Optimizing extender unit supply and host metabolism.

Main Results:

• Successful engineering of a PKS pathway for adipic acid production.
• Demonstrated selective succinyl-CoA loading *in vivo* using the EtnB module.
• Achieved functional expression of a highly chimeric PKS with domains from seven modules across six non-natural junctions.
• Enhanced AA titers through additional engineering strategies.

Conclusions:

• Highly chimeric PKS systems can be functionally engineered through rational design.
• The carboxyl-retaining EtnB module expands the PKS toolkit for dicarboxylic acid synthesis.
• This work establishes a versatile platform for engineering diacids and other noncanonical products using PKS pathways.