A Cytochrome b(5)-Containing Plastid-Located Fatty Acid Desaturase from Chlamydomonas reinhardtii

作者：Zaeuner Simone; Jochum Wibke; Bigorowski Tara; Benning Christoph^*

来源：Eukaryotic Cell, 2012, 11(7): 856-863.

DOI：10.1128/EC.00079-12

Monogalactosyldiacylglycerol (MGDG) in Chlamydomonas reinhardtii and other green algae contains hexadeca-4,7,10,13-tetraenoic acid (16:4) in the glycerol sn-2 position. While many genes necessary for the introduction of acyl chain double bonds have been functionally characterized, the Delta 4-desaturase remained unknown. Using a phylogenetic comparison, a candidate gene encoding the MGDG-specific Delta 4-desaturase from Chlamydomonas (Cr Delta 4FAD) was identified. Cr Delta 4FAD shows all characteristic features of a membrane-bound desaturase, including three histidine boxes and a transit peptide for chloroplast targeting. But it also has an N-terminal cytochrome b(5) domain, distinguishing it from other known plastid desaturases. Cytochrome b(5) is the primary electron donor for endoplasmic reticulum (ER) desaturases and is often fused to the desaturase domain in desaturases modifying the carboxyl end of the acyl group. Difference absorbance spectra of the recombinant cytochrome b(5) domain of Cr Delta 4FAD showed that it is functional in vitro. Green fluorescent protein fusions of Cr Delta 4FAD localized to the plastid envelope in Chlamydomonas. Interestingly, overproduction of Cr Delta 4FAD in Chlamydomonas not only increased levels of 16: 4 acyl groups in cell extracts but specifically increased the total amount of MGDG. Vice versa, the amount of MGDG was lowered in lines with reduced levels of Cr Delta 4FAD. These data suggest a link between MGDG molecular species composition and galactolipid abundance in the alga, as well as a specific function for this fatty acid in MGDG.

• 出版日期2012-7