title: Structure/function analysis of a type iii polyketide synthase in the brown alga Ectocarpus siliculosus reveals a biochemical pathway in phlorotannin monomer biosynthesis.
abstract: Brown algal phlorotannins are structural analogs of condensed tannins in terrestrial plants and, like plant phenols, they have numerous biological functions. Despite their importance in brown algae, phlorotannin biosynthetic pathways have been poorly characterized at the molecular level. We found that a predicted type III polyketide synthase in the genome of the brown alga Ectocarpus siliculosus, PKS1, catalyzes a major step in the biosynthetic pathway of phlorotannins (i.e., the synthesis of phloroglucinol monomers from malonyl-CoA). The crystal structure of PKS1 at 2.85-Å resolution provided a good quality electron density map showing a modified Cys residue, likely connected to a long chain acyl group. An additional pocket not found in other known type III PKSs contains a reaction product that might correspond to a phloroglucinol precursor. In vivo, we also found a positive correlation between the phloroglucinol content and the PKS III gene expression level in cells of a strain of Ectocarpus adapted to freshwater during its reacclimation to seawater. The evolution of the type III PKS gene family in Stramenopiles suggests a lateral gene transfer event from an actinobacterium.
authors: Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7139, Station Biologique de Roscoff, 29688 Roscoff cedex, Brittany, France.
authors: Laurence
authors: L
authors: Meslet-Cladière
authors: Ludovic
authors: L
authors: Delage
authors: Cédric J-J
authors: CJ
authors: Leroux
authors: Sophie
authors: S
authors: Goulitquer
authors: Catherine
authors: C
authors: Leblanc
authors: Emeline
authors: E
authors: Creis
authors: Erwan Ar
authors: EA
authors: Gall
authors: Valérie
authors: V
authors: Stiger-Pouvreau
authors: Mirjam
authors: M
authors: Czjzek
authors: Philippe
authors: P
authors: Potin
mesh_terms: D000064:Acclimatization; D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D005618:Fresh Water; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000459:Phaeophyceae / Q000201:enzymology* / Q000235:genetics; D010696:Phloroglucinol / Q000737:chemistry / Q000378:metabolism; D010802:Phylogeny; D048630:Polyketide Synthases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012623:Seawater; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D013634:Tannins / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D012333:RNA, Messenger; D011994:Recombinant Proteins; D013634:Tannins; D048630:Polyketide Synthases; D010696:Phloroglucinol
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