title: Enantioselective regulation of lactate racemization by LarR in Lactobacillus plantarum.
abstract: Lactobacillus plantarum is a lactic acid bacterium that produces a racemic mixture of l- and d-lactate from sugar fermentation. The interconversion of lactate isomers is performed by a lactate racemase (Lar) that is transcriptionally controlled by the l-/d-lactate ratio and maximally induced in the presence of l-lactate. We previously reported that the Lar activity depends on the expression of two divergently oriented operons: (i) the larABCDE operon encodes the nickel-dependent lactate racemase (LarA), its maturases (LarBCE), and a lactic acid channel (LarD), and (ii) the larR(MN)QO operon encodes a transcriptional regulator (LarR) and a four-component ABC-type nickel transporter [Lar(MN), in which the M and N components are fused, LarQ, and LarO]. LarR is a novel regulator of the Crp-Fnr family (PrfA group). Here, the role of LarR was further characterized in vivo and in vitro. We show that LarR is a positive regulator that is absolutely required for the expression of Lar activity. Using gel retardation experiments, we demonstrate that LarR binds to a 16-bp palindromic sequence (Lar box motif) that is present in the larR-larA intergenic region. Mutations in the Lar box strongly affect LarR binding and completely abolish transcription from the larA promoter (PlarA). Two half-Lar boxes located between the Lar box and the -35 box of PlarA promote LarR multimerization on DNA, and point mutations within one or both half-Lar boxes inhibit PlarA induction by l-lactate. Gel retardation and footprinting experiments indicate that l-lactate has a positive effect on the binding and multimerization of LarR, while d-lactate antagonizes the positive effect of l-lactate. A possible mechanism of LarR regulation by lactate enantiomers is proposed.
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Benoît
authors.initials: B
authors.lastname: Desguin
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Philippe
authors.initials: P
authors.lastname: Goffin
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Nordine
authors.initials: N
authors.lastname: Bakouche
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Diman
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Eric
authors.initials: E
authors.lastname: Viaene
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Damien
authors.initials: D
authors.lastname: Dandoy
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Fontaine
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Hallet
authors.affiliation: Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve, Belgium pascal.hols@uclouvain.be.
authors.forename: Pascal
authors.initials: P
authors.lastname: Hols
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial; D021901:DNA, Intergenic; D024202:Electrophoretic Mobility Shift Assay; D005285:Fermentation; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D019344:Lactic Acid / Q000737:chemistry / Q000378:metabolism*; D048191:Lactiplantibacillus plantarum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D019998:Racemases and Epimerases / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D021901:DNA, Intergenic; D019344:Lactic Acid; D019998:Racemases and Epimerases; C021498:lactate racemase