Dissecting the Functional Role of Polyketide Synthases in Dictyostelium discoideum

Abstract

Dictyostelium discoideum exhibits the largest repository of polyketide synthase (PKS) proteins of all known genomes. However, the functional relevance of these proteins in the biology of this organism remains largely obscure. On the basis of computational, biochemical, and gene expression studies, we propose that the multifunctional Dictyostelium PKS (DiPKS) protein DiPKS1 could be involved in the biosynthesis of the differentiation regulating factor 4-methyl-5-pentylbenzene-1,3-diol (MPBD). Our cell-free reconstitution studies of a novel acyl carrier protein Type III PKS didomain from DiPKS1 revealed a crucial role of protein-protein interactions in determining the final biosynthetic product. Whereas the Type III PKS domain by itself primarily produces acyl pyrones, the presence of the interacting acyl carrier protein domain modulates the catalytic activity to produce the alkyl resorcinol scaffold of MPBD. Furthermore, we have characterized an O-methyltransferase (OMT12) from Dictyostelium with the capability to modify this resorcinol ring to synthesize a variant of MPBD. We propose that such a modification in vivo could in fact provide subtle variations in biological function and specificity. In addition, we have performed systematic computational analysis of 45 multidomain PKSs, which revealed several unique features in DiPKS proteins. Our studies provide a new perspective in understanding mechanisms by which metabolic diversity could be generated by combining existing functional scaffolds.

Cyclization of aromatic polyketides from bacteria and fungi

“…During the biosynthesis of 164 , two rounds of C2–C7 cyclization were proposed to be performed by the enzymes. To conclude discussion of resorcinol biosynthesis, it is worth mentioning that an alkylresorcinol-producing enzyme (Steely1 or DiPKS1) was discovered in the social amoeba Dictyostelium discoideum , a primitive eukaryote 198,199. Steely1 is a hybrid megasynthases in which a type III PKS is appended at the C -terminus of a type I iterative PKS.…”

“…Steely1 is a hybrid megasynthases in which a type III PKS is appended at the C -terminus of a type I iterative PKS. Steely1 synthesizes the differentiation regulating factor 4-methyl-5-pentylbenzene-1,3-diol (MPBD, 165 ) 199. The crystal structure of the type III PKS domain of Steely1 showed a conserved αβαβα-fold and a didomain architecture characteristic of other type III PKSs 198.…”

Identification and Characterization of a Type III Polyketide Synthase Involved in Quinolone Alkaloid Biosynthesis from Aegle marmelos Correa

“…The diversity observed with type III PKS arises from its ability to accept variety of acyl-CoA thioesters for priming the reaction, its capability to extend this starter with variable number of extender units and also perform different cyclizations of the poly-␤-keto linear polyketide intermediate. Although type III PKS have been studied in plants for decades, genome sequencing projects has resulted in identification of type III PKS homologues from several bacteria, fungi, and lower eukaryotes (15). Interestingly, the first report of a type III PKS accepting long chain acyl-CoA substrates was reported from a bacterium, Mycobacterium tuberculosis (16).…”

The Hybrid Type Polyketide Synthase SteelyA Is Required for cAMP Signalling in Early Dictyostelium Development

“…Previously, two distinct patterns of stlA gene expression were reported: one of them was that the gene was expressed during the early stage development [17], whereas another one was that the gene was expressed during only late stage [24]. We resolved these conflicting reports concerning the gene expression pattern, by re-examining the expression pattern with by RT-PCR using two different primer sets.…”