Functions of the Clostridium acetobutylicium FabF and FabZ proteins in unsaturated fatty acid biosynthesis.
BACKGROUND
The original anaerobic unsaturated fatty acid biosynthesis pathway proposed by Goldfine and Bloch was based on in vivo labeling studies in Clostridium butyricum ATCC 6015 (now C. beijerinckii) but to date no dedicated unsaturated fatty acid biosynthetic enzyme has been identified in Clostridia. C. acetobutylicium synthesizes the same species of unsaturated fatty acids as E. coli, but lacks all of the known unsaturated fatty acid synthetic genes identified in E. coli and other bacteria. A possible explanation was that two enzymes of saturated fatty acid synthesis of C. acetobutylicium, FabZ and FabF might also function in the unsaturated arm of the pathway (a FabZ homologue is known to be an unsaturated fatty acid synthetic enzyme in enterococci).


RESULTS
We report that the FabF homologue located within the fatty acid biosynthetic gene cluster of C. acetobutylicium functions in synthesis of both unsaturated fatty acids and saturated fatty acids. Expression of this protein in E. coli functionally replaced both the FabB and FabF proteins of the host in vivo and replaced E. coli FabB in a defined in vitro fatty acid synthesis system. In contrast the single C. acetobutylicium FabZ homologue, although able to functionally replace E. coli FabZ in vivo and in vitro, was unable to replace FabA, the key dehydratase-isomerase of E. coli unsaturated fatty acid biosynthesis in vivo and lacked isomerase activity in vitro.


CONCLUSIONS
Thus, C. acetobutylicium introduces the double of unsaturated fatty acids by use of a novel and unknown enzyme.
Zhu
Lei
L
College of Life Science, South China Agricultural University, Guangzhou 510642, PR China. vermilionrock@yahoo.com
Cheng
Juanli
J
Luo
Biao
B
Feng
Saixiang
S
Lin
Jinshui
J
Wang
Shengbin
S
Cronan
John E
JE
Wang
Haihong
H
D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D046969:Clostridium acetobutylicum / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005810:Multigene Family
D001426:Bacterial Proteins; D005231:Fatty Acids, Unsaturated; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase