The <Emphasis Type="Italic">Lactococcus lactis</Emphasis> FabF fatty acid synthetic enzyme can functionally replace both the FabB and FabF proteins of <Emphasis Type="Italic">Escherichia coli</Emphasis> and the FabH protein of <Emphasis Type="Italic">Lactococcus lactis</Emphasis> |
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Authors: | Rachael M Morgan-Kiss John E Cronan |
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Institution: | (1) Department of Microbiology, B103 Chemical and Life Sciences Laboratory, University of Illinois at Urbana-Champaign, 601 S. Goodwin Ave., Urbana, IL 61801, USA;(2) Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA;(3) Present address: Department of Microbiology, Miami University, Pearson Hall, 44, Oxford, OH 45056, USA |
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Abstract: | The genome of Lactococcus lactis encodes a single long chain 3-ketoacyl-acyl carrier protein synthase. This is in contrast to its close relative, Enterococcus faecalis, and to Escherichia coli, both of which have two such enzymes. In E. faecalis and E. coli, one of the two long chain synthases (FabO and FabB, respectively) has a role in unsaturated fatty acid synthesis that cannot
be satisfied by FabF, the other long chain synthase. Since L. lactis has only a single long chain 3-ketoacyl-acyl carrier protein synthase (annotated as FabF), it seemed likely that this enzyme
must function both in unsaturated fatty acid synthesis and in elongation of short chain acyl carrier protein substrates to
the C18 fatty acids found in the cellular phospholipids. We report that this is the case. Expression of L. lactis FabF can functionally replace both FabB and FabF in E. coli, although it does not restore thermal regulation of phospholipid fatty acid composition to E. coli
fabF mutant strains. The lack of thermal regulation was predictable because wild-type L. lactis was found not to show any significant change in fatty acid composition with growth temperature. We also report that overproduction
of L. lactis FabF allows growth of an L. lactis mutant strain that lacks the FabH short chain 3-ketoacyl-acyl carrier protein synthase. The strain tested was a derivative
(called the ∆fabH bypass strain) of the original fabH deletion strain that had acquired the ability to grow when supplemented with octanoate. Upon introduction of a FabF overexpression
plasmid into this strain, growth proceeded normally in the absence of fatty acid supplementation. Moreover, this strain had
a normal rate of fatty acid synthesis and a normal fatty acid composition. Both the ∆fabH bypass strain that overproduced FabF and the wild type strain incorporated much less exogenous octanoate into long chain
phospholipid fatty acids than did the ∆fabH bypass strain. Incorporation of octanoate and decanoate labeled with deuterium showed that these acids were incorporated
intact as the distal methyl and methylene groups of the long chain fatty acids. |
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Keywords: | Lactococcus lactis Fatty acid synthesis 3-Ketoacyl-ACP synthases |
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