A bifunctional Delta12,Delta15-desaturase from Acanthamoeba castellanii directs the synthesis of highly unusual n-1 series unsaturated fatty acids.
The free-living soil protozoon Acanthamoeba castellanii synthesizes a range of polyunsaturated fatty acids, the balance of which can be altered by environmental changes. We have isolated and functionally characterized in yeast a microsomal desaturase from A. castellanii, which catalyzes the sequential conversion of C(16) and C(18) Delta9-monounsaturated fatty acids to di- and tri-unsaturated forms. In the case of C(16) substrates, this bifunctional A. castellanii Delta12,Delta15-desaturase generated a highly unusual fatty acid, hexadecatrienoic acid (16:3Delta(9,12,15)(n-1)). The identification of a desaturase, which can catalyze the insertion of a double bond between the terminal two carbons of a fatty acid represents a new addition to desaturase functionality and plasticity. We have also co-expressed in yeast the A. castellanii bifunctional Delta12,Delta15-desaturase with a microsomal Delta6-desaturase, resulting in the synthesis of the highly unsaturated C(16) fatty acid hexadecatetraenoic acid (16:4Delta(6,9,12,15)(n-1)), previously only reported in marine microorganisms. Our work therefore demonstrates the feasibility of the heterologous synthesis of polyunsaturated fatty acids of the n-1 series. The presence of a bifunctional Delta12,Delta15-desaturase in A. castellanii is also considered with reference to the evolution of desaturases and the lineage of this protist.
Sayanova
Olga
O
Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom.
Haslam
Richard
R
Guschina
Irina
I
Lloyd
David
D
Christie
William W
WW
Harwood
John L
JL
Napier
Johnathan A
JA
D048248:Acanthamoeba castellanii / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D020224:Expressed Sequence Tags; D044943:Fatty Acid Desaturases / Q000737:chemistry*; D005227:Fatty Acids / Q000096:biosynthesis* / Q000737:chemistry; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013997:Time Factors
D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D008055:Lipids; D044943:Fatty Acid Desaturases; C040448:delta-12 fatty acid desaturase; C094563:delta-15 desaturase