title: A new mechanism for anaerobic unsaturated fatty acid formation in Streptococcus pneumoniae.
abstract: The anaerobic pathway for unsaturated fatty acid synthesis was established in the 1960s in Escherichia coli. The double bond is introduced into the growing acyl chain by FabA, an enzyme capable of both the dehydration of beta-hydroxydecanoyl-acyl carrier protein (ACP) to trans-2-decenoyl-ACP, and the isomerization of trans-2 to cis-3-decenoyl-ACP. However, there are a number of anaerobic bacteria whose genomes do not contain a fabA homolog, although these organisms nonetheless produce unsaturated fatty acids. We cloned and biochemically characterized a new enzyme in type II fatty acid synthesis from Streptococcus pneumoniae that carries out the isomerization of trans-2-decenoyl-ACP to cis-3-decenoyl-ACP, but is not capable of catalyzing the dehydration of beta-hydroxy intermediates. This tetrameric enzyme, designated FabM, has no similarity to FabA, but rather is a member of the hydratase/isomerase superfamily. Thus, the branch point in the biosynthesis of unsaturated fatty acids in S. pneumoniae occurs following the formation of trans-2-decenoyl-ACP, in contrast to E. coli where the branch point takes place after the formation of beta-hydroxydecanoyl-ACP.
authors.affiliation: Department of Infectious Diseases, Protein Science Division, St Jude Children's Research Hospital, Memphis, Tennessee 38105-2794, USA.
authors.forename: Hedia
authors.initials: H
authors.lastname: Marrakchi
authors.forename: Keum-Hwa
authors.initials: KH
authors.lastname: Choi
authors.forename: Charles O
authors.initials: CO
authors.lastname: Rock
mesh_terms: D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D005816:Genetic Complementation Test; D006836:Hydro-Lyases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007535:Isomerases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D005810:Multigene Family; D010100:Oxygen / Q000378:metabolism*; D016415:Sequence Alignment; D021241:Spectrometry, Mass, Electrospray Ionization; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D005231:Fatty Acids, Unsaturated; D006836:Hydro-Lyases; D007535:Isomerases; D010100:Oxygen