Chain initiation on the soraphen-producing modular polyketide synthase from Sorangium cellulosum

Area of Science:

• Biochemistry
• Molecular Biology
• Synthetic Biology

Background:

• Polyketides are diverse natural products synthesized by bacterial modular polyketide synthases (PKSs).
• PKSs utilize specific loading modules to select starter units for polyketide chain extension.
• The soraphen PKS employs an unusual loading module specifying a benzoic acid starter unit.

Purpose of the Study:

• To investigate the functional transfer of the soraphen PKS loading module's starter unit specificity to other PKSs.
• To test the understanding of PKS domain interactions and substrate recruitment in hybrid enzyme construction.

Main Methods:

• Construction of hybrid PKSs by substituting domains from the soraphen PKS into the DEBS1-TE scaffold.
• Analysis of product formation from hybrid PKSs, including engineered acyltransferase (AT) domains and loading modules.
• Manipulation of intracellular benzoyl-CoA levels in the host strain (Saccharopolyspora erythraea).

Main Results:

• Hybrid PKSs with soraphen AT domains successfully produced triketide lactones with altered structures.
• Incorporation of the soraphen loading module led to 5-phenyl-substituted triketide lactone production.
• Production of phenyl-substituted lactones was dependent on increased intracellular benzoyl-CoA supply.

Conclusions:

• The ability to recruit a benzoate starter unit can be conferred by transferring specific AT domains or modules from the soraphen PKS.
• Successful benzoate incorporation into hybrid PKS products necessitates the availability of benzoyl-CoA precursor.
• Engineering hybrid actinomycete-myxobacterial PKSs expands the synthetic capabilities of these enzymes.