Functions of the Clostridium acetobutylicium FabF and FabZ proteins in unsaturated fatty acid biosynthesis

Lei Zhu,Jinshui Lin,John E Cronan,Saixiang Feng,Haihong Wang,Shengbin Wang,Biao Luo,Juanli Cheng

doi:10.1186/1471-2180-9-119

Abstract

BackgroundThe 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).ResultsWe 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.ConclusionThus, C. acetobutylicium introduces the double of unsaturated fatty acids by use of a novel and unknown enzyme.

Highlights

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 ( C. beijerinckii) but to date no dedicated unsaturated fatty acid biosynthetic enzyme has been identified in Clostridia
BMC Microbiology 2009, 9:119 http://www.biomedcentral.com/1471-2180/9/119 option for anaerobically grown bacteria [3]. These investigators originally proposed that introduction of the double bond involved a direct dehydration of the 3-hydroxydecanoyl intermediate of fatty acid synthesis to give a cis-3 double bond which would be conserved though subsequent cycles of addition of two carbon atoms to give the membrane lipid unsaturated fatty acids (UFAs) moieties [4]
Only fabF1 complemented the E. coli fabF mutation showing that C. acetobutylicium FabF1, like E. coli FabF, is able to catalyze all of the elongation reactions required in the synthesis of saturated fatty acids

Summary

Introduction

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 ( C. beijerinckii) but to date no dedicated unsaturated fatty acid biosynthetic enzyme has been identified in Clostridia. BMC Microbiology 2009, 9:119 http://www.biomedcentral.com/1471-2180/9/119 option for anaerobically grown bacteria [3] These investigators originally proposed that introduction of the double bond involved a direct dehydration of the 3-hydroxydecanoyl intermediate of fatty acid synthesis to give a cis-3 double bond which would be conserved though subsequent cycles of addition of two carbon atoms to give the membrane lipid UFA moieties [4]. C. acetobutylicium lacks fabM, fabA and fabB and has only a single copy of fabZ, its fatty acid composition is similar to that of E. coli This bacterium contains three genes that encode putative FabFs, only one of these seemed likely to be involved in fatty acid synthesis (see Discussion). The single FabF homologue active in fatty acid synthesis has the functions of both E. coli long chain 3-ketoacyl-ACP synthases, FabB and FabF

Methods

Results

Discussion

Conclusion