Physcomitrella PpORS, Basal to Plant Type III Polyketide Synthases in Phylogenetic Trees, Is a Very Long Chain 2′-Oxoalkylresorcinol Synthase

• Published in: The Journal of biological chemistry Vol. 288; no. 4; pp. 2767 - 2777
• Main Authors: Kim, Sun Young, Colpitts, Che C., Wiedemann, Gertrud, Jepson, Christina, Rahimi, Mehrieh, Rothwell, Jordan R., McInnes, Adam D., Hasebe, Mitsuyasu, Reski, Ralf, Sterenberg, Brian T., Suh, Dae-Yeon
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25.01.2013; American Society for Biochemistry and Molecular Biology
• Subjects: 2′-Oxoalkylresorcinol Synthase; Acyl Coenzyme A - chemistry; Binding Sites; Biosynthesis; Bryopsida - metabolism; Catalysis; Catalytic Domain; Cloning, Molecular; Enzymes; Enzymology; Expressed Sequence Tags; Gene Expression Regulation, Enzymologic; Kinetics; Models, Chemical; Mutagenesis, Site-Directed; Mutation; Natural Product Biosynthesis; Oligonucleotide Array Sequence Analysis; Phylogeny; Physcomitrella; Plant Biochemistry; Polyketide Synthases - chemistry; Polyketide Synthases - metabolism; Polyketides; Protein Binding; Protein Evolution; Recombinant Proteins - chemistry; Type III Polyketide Synthase; Very Long Chain Fatty Acyl-CoA; Natural Product Biosynthesis; Enzymes; 2′-Oxoalkylresorcinol Synthase; Plant Biochemistry; Polyketides; Physcomitrella; Very Long Chain Fatty Acyl-CoA; Biosynthesis; Protein Evolution; Type III Polyketide Synthase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.430686

The plant type III polyketide synthases (PKSs), which produce diverse secondary metabolites with different biological activities, have successfully co-evolved with land plants. To gain insight into the roles that ancestral type III PKSs played during the early evolution of land plants, we cloned and characterized PpORS from the moss Physcomitrella. PpORS has been proposed to closely resemble the most recent common ancestor of the plant type III PKSs. PpORS condenses a very long chain fatty acyl-CoA with four molecules of malonyl-CoA and catalyzes decarboxylative aldol cyclization to yield the pentaketide 2′-oxoalkylresorcinol. Therefore, PpORS is a 2′-oxoalkylresorcinol synthase. Structure modeling and sequence alignments identified a unique set of amino acid residues (Gln218, Val277, and Ala286) at the putative PpORS active site. Substitution of the Ala286 to Phe apparently constricted the active site cavity, and the A286F mutant instead produced triketide alkylpyrones from fatty acyl-CoA substrates with shorter chain lengths. Phylogenetic analysis and comparison of the active sites of PpORS and alkylresorcinol synthases from sorghum and rice suggested that the gramineous enzymes evolved independently from PpORS to have similar functions but with distinct active site architecture. Microarray analysis revealed that PpORS is exclusively expressed in nonprotonemal moss cells. The in planta function of PpORS, therefore, is probably related to a nonprotonemal structure, such as the cuticle. Background:Physcomitrella PpORS is an ancient member of the plant type III polyketide synthase (PKS) family. Results: PpORS, produced in nonprotonemal moss cells, synthesizes pentaketide 2′-oxoalkylresorcinols using a unique substrate binding site. Conclusion: PpORS is a novel very long chain 2′-oxoalkylresorcinol synthase. Significance: This is the first step toward understanding the co-evolution of the type III PKS family and land plants.