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Identification and functional characterization of the moss Physcomitrella patens delta5-desaturase gene involved in arachidonic and eicosapentaenoic acid biosynthesis.

Kaewsuwan S, Cahoon EB, Perroud PF, Wiwat C, Panvisavas N, Quatrano RS, Cove DJ, Bunyapraphatsara N

Department of Pharmacognosy, Faculty of Pharmacy, Mahidol University, 447 Sri-Ayudhya Road, Ratchathewi, Bangkok 10400, Thailand.

The moss Physcomitrella patens contains high levels of arachidonic acid and lesser amounts of eicosapentaenoic acid. Here we report the identification and characterization of a delta5-desaturase from P. patens that is associated with the synthesis of these fatty acids. A full-length cDNA for this desaturase was identified by data base searches based on homology to sequences of known delta5-desaturase cDNAs from fungal and algal species. The resulting P. patens cDNA encodes a 480-amino acid polypeptide that contains a predicted N-terminal cytochrome b5-like domain as well as three histidine-rich domains. Expression of the enzyme in Saccharomyces cerevisiae resulted in the production of the delta5-containing fatty acid arachidonic acid in cells that were provided di-homo-gamma-linolenic acid. In addition, the expressed enzyme generated delta5-desaturation products with the C20 substrates omega-6 eicosadienoic and omega-3 eicosatrienoic acids, but no products were detected with the C18 fatty acid linoleic and alpha-linolenic acids or with the C22 fatty acid adrenic and docosapentaenoic acids. When the corresponding P. patens genomic sequence was disrupted by replacement through homologous recombination, a dramatic alteration in the fatty acid composition was observed, i.e. an increase in di-homo-gamma-linolenic and eicosatetraenoic acids accompanied by a concomitant disappearance of the delta5-fatty acid arachidonic and eicosapentaenoic acids. In addition, overexpression of the P. patens cDNA in protoplasts isolated from a disrupted line resulted in the restoration of arachidonic acid synthesis.

Published 31 July 2006 in J Biol Chem, 281(31): 21988-97.
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