摘要：SummaryType I polyketide synthases (PKSs) are multidomain, multimodule enzymes capable of producing complex polyketide metabolites. These modules contain an acyltransferase (AT) domain, which selects acyl-CoA substrates to be incorporated into the metabolite scaffold. Herein, we reveal the sequences of three AT domains from a polyketide synthase (TgPKS2) from the apicomplexan parasiteToxoplasma gondii. Phylogenic analysis indicates these ATs (AT1, AT2, and AT3) are distinct from domains in well-characterized microbial biosynthetic gene clusters. Biochemical investigations revealed that AT1 and AT2 hydrolyze malonyl-CoA but the terminal AT3 domain is non-functional. We further identify an “on-off switch” residue that controls activity such that a single amino acid change in AT3 confers hydrolysis activity while the analogous mutation in AT2 eliminates activity. This biochemical analysis of AT domains from an apicomplexan PKS lays the foundation for further molecular and structural studies on PKSs fromT. gondiiand other protists.Graphical abstractDisplay OmittedHighlights•The apicomplexan parasiteT. gondiiencodes a type I polyketide synthase,TgPKS2•TgPKS2 has 3 acyltransferase (AT) domains with predicted selectivity for malonyl-CoA•AT1 and AT2 hydrolyze malonyl-CoAin vitro, while the AT3 domain is inactive•A single amino acid serves as an “on-off switch” residue that enables AT activityBiological sciences; Biochemistry; Structural biology
