Submitted to: Lipids Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2007
Publication Date: 8/7/2007
Citation: He, X., Chen, G.Q., Kang, S.T., Mckeon, T.A. 2007. Ricinus communis contains and acyl-CoA synthetase that preferentially activates ricinoleate to its CoA thioester. Lipids Journal. 42:931-938. Interpretive Summary: Castor oil is widely used in the chemical industry as a feedstock for producing high-end plastics, it would be useful to engineer a temperate oilseed crop to produce ricinoleic acid. Therefore, we need to understand how the castor plant is able to make such an unusual fatty acid. The study reported in this manuscript provides us with the biochemical tools we need to understand an important biochemical step in castor oil synthesis. The ability to make a high ricinoleic oil will support expanded development of bio-based products - manufactured products whose raw materials are derived from plants and other renewable sources. Such materials will retain their environmentally friendly properties while replacing products derived from petroleum.
Technical Abstract: As part of our effort to identify enzymes that are critical for producing large amounts of ricinoleate in castor oil, we have isolated three cDNAs encoding acyl-CoA synthetase (ACS) in the castor plant. Analysis of the cDNA sequences reveals that two of them, designated RcACS 2 and RcACS 4, contain complete coding regions corresponding to 694 and 690 amino acids, respectively. The third cDNA, RcACS 1, encodes a truncated gene sequence. The RcACS 2 and RcACS 4 share 77% identity at the amino acid sequence level. Complementation tests showed that both RcACS 2 and RcACS 4 successfully restored growth of a yeast mutant strain (YB525) deficient in ACS. Lysates from yeast cells expressing RcACS 2 and 4 were enzymatically active when using 14C-labeled oleic acid as a substrate. Cell fractionation study indicates that RcACS 2 and 4 are mainly associated with membranes. Substrate specificity assays indicate that the RcACS 2 preferentially activates ricinoleate, while the RcACS 4 has a preference for nonhydroxy fatty acids.