Basidiomycete non-reducing polyketide synthases function independently of SAT domains

Area of Science:

• Biochemistry
• Molecular Biology
• Mycology

Background:

• Non-reducing polyketide synthases (NR-PKSs) are key enzymes in fungal natural product biosynthesis, diversifying compounds in Asco- and Basidiomycota.
• NR-PKSs traditionally initiate polyketide synthesis via an N-terminal starter unit:acyl transferase (SAT) domain, transferring an acetyl group to the acyl carrier protein (ACP).

Purpose of the Study:

• To investigate the functional necessity of the SAT domain in NR-PKSs across different fungal lineages.
• To characterize novel NR-PKSs from a newly identified twelfth clade.

Main Methods:

• Phylogenetic analysis of NR-PKS sequences.
• Biochemical characterization of wild-type and SAT-domainless NR-PKS variants in vivo and in vitro.
• Comparative analysis of ascomycete and basidiomycete NR-PKSs.

Main Results:

• A twelfth clade of NR-PKSs was identified, with characterized enzymes from Cortinarius rufoolivaceus lacking a functional SAT domain but remaining active.
• SAT-domainless NR-PKSs from Basidiomycota (clade VIII) retained full enzymatic activity.
• A SAT-domainless ascomycete NR-PKS (ACAS) was inactive, suggesting lineage-specific roles for the SAT domain.

Conclusions:

• The SAT domain is dispensable for the function of many basidiomycete NR-PKSs, unlike in ascomycetes.
• This understanding can guide the engineering of more efficient NR-PKS systems for synthetic biology.
• Genomic identification of SAT-domainless NR-PKS genes should be considered for fungal natural product potential, avoiding misclassification as pseudogenes.