title: PTS-Mediated Regulation of the Transcription Activator MtlR from Different Species: Surprising Differences despite Strong Sequence Conservation.
abstract: The hexitol D-mannitol is transported by many bacteria via a phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS). In most Firmicutes, the transcription activator MtlR controls the expression of the genes encoding the D-mannitol-specific PTS components and D-mannitol-1-P dehydrogenase. MtlR contains an N-terminal helix-turn-helix motif followed by an Mga-like domain, two PTS regulation domains (PRDs), an EIIB(Gat)- and an EIIA(Mtl)-like domain. The four regulatory domains are the target of phosphorylation by PTS components. Despite strong sequence conservation, the mechanisms controlling the activity of MtlR from Lactobacillus casei, Bacillus subtilis and Geobacillus stearothermophilus are quite different. Owing to the presence of a tyrosine in place of the second conserved histidine (His) in PRD2, L. casei MtlR is not phosphorylated by Enzyme I (EI) and HPr. When the corresponding His in PRD2 of MtlR from B. subtilis and G. stearothermophilus was replaced with alanine, the transcription regulator was no longer phosphorylated and remained inactive. Surprisingly, L. casei MtlR functions without phosphorylation in PRD2 because in a ptsI (EI) mutant MtlR is constitutively active. EI inactivation prevents not only phosphorylation of HPr, but also of the PTS(Mtl) components, which inactivate MtlR by phosphorylating its EIIB(Gat)- or EIIA(Mtl)-like domain. This explains the constitutive phenotype of the ptsI mutant. The absence of EIIB(Mtl)-mediated phosphorylation leads to induction of the L. caseimtl operon. This mechanism resembles mtlARFD induction in G. stearothermophilus, but differs from EIIA(Mtl)-mediated induction in B. subtilis. In contrast to B. subtilis MtlR, L. casei MtlR activation does not require sequestration to the membrane via the unphosphorylated EIIB(Mtl) domain.
authors.affiliation: INRA, Microbiologie de l'alimentation au service de la santé humaine (MICALIS), UMR1319, Jouy en Josas, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Joyet
authors.forename: Meriem
authors.initials: M
authors.lastname: Derkaoui
authors.forename: Houda
authors.initials: H
authors.lastname: Bouraoui
authors.forename: Josef
authors.initials: J
authors.lastname: Deutscher
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D017124:Conserved Sequence; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D001411:Geobacillus stearothermophilus / Q000235:genetics / Q000378:metabolism; D007780:Lacticaseibacillus casei / Q000235:genetics / Q000378:metabolism*; D008353:Mannitol / Q000378:metabolism; D009876:Operon; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C085654:MtlR protein, E coli; D012097:Repressor Proteins; D008353:Mannitol; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System