title: Physcomitrella PpORS, basal to plant type III polyketide synthases in phylogenetic trees, is a very long chain 2'-oxoalkylresorcinol synthase.
abstract: 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 (Gln(218), Val(277), and Ala(286)) at the putative PpORS active site. Substitution of the Ala(286) 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Che C
authors.initials: CC
authors.lastname: Colpitts
authors.forename: Gertrud
authors.initials: G
authors.lastname: Wiedemann
authors.forename: Christina
authors.initials: C
authors.lastname: Jepson
authors.forename: Mehrieh
authors.initials: M
authors.lastname: Rahimi
authors.forename: Jordan R
authors.initials: JR
authors.lastname: Rothwell
authors.forename: Adam D
authors.initials: AD
authors.lastname: McInnes
authors.forename: Mitsuyasu
authors.initials: M
authors.lastname: Hasebe
authors.forename: Ralf
authors.initials: R
authors.lastname: Reski
authors.forename: Brian T
authors.initials: BT
authors.lastname: Sterenberg
authors.forename: Dae-Yeon
authors.initials: DY
authors.lastname: Suh
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry; D001665:Binding Sites; D019068:Bryopsida / Q000378:metabolism*; D002384:Catalysis; D020134:Catalytic Domain; D003001:Cloning, Molecular; D020224:Expressed Sequence Tags; D015971:Gene Expression Regulation, Enzymologic; D007700:Kinetics; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D048630:Polyketide Synthases / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D000214:Acyl Coenzyme A; D011994:Recombinant Proteins; D048630:Polyketide Synthases