title: Mannitol-1-phosphate dehydrogenases/phosphatases: a family of novel bifunctional enzymes for bacterial adaptation to osmotic stress.
abstract: The nutritionally versatile soil bacterium Acinetobacter baylyi ADP1 copes with salt stress by the accumulation of compatible solutes, a strategy that is widespread in nature. This bacterium synthesizes the sugar alcohol mannitol de novo in response to osmotic stress. In a previous study, we identified MtlD, a mannitol-1-phosphate dehydrogenase, which is essential for mannitol biosynthesis and which catalyses the first step in mannitol biosynthesis, the reduction of fructose-6-phosphate (F-6-P) to the intermediate mannitol-1-phosphate (Mtl-1-P). Until now, the identity of the second enzyme, the phosphatase that catalyses the dephosphorylation of Mtl-1-P to mannitol, was elusive. Here we show that MtlD has a unique sequence among known mannitol-1-phosphate dehydrogenases with a haloacid dehalogenase (HAD)-like phosphatase domain at the N-terminus. This domain is indeed shown to have a phosphatase activity. Phosphatase activity is strictly Mg(2+) dependent. Nuclear magnetic resonance analysis revealed that purified MtlD catalyses not only reduction of F-6-P but also dephosphorylation of Mtl-1-P. MtlD of A. baylyi is the first bifunctional enzyme of mannitol biosynthesis that combines Mtl-1-P dehydrogenase and phosphatase activities in a single polypeptide chain. Bioinformatic analysis revealed that the bifunctional enzyme is widespread among Acinetobacter strains but only rarely present in other phylogenetic tribes.
authors.affiliation: Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt am Main, Frankfurt, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Sand
authors.forename: Marta
authors.initials: M
authors.lastname: Rodrigues
authors.forename: José M
authors.initials: JM
authors.lastname: González
authors.forename: Valérie
authors.initials: V
authors.lastname: de Crécy-Lagard
authors.forename: Helena
authors.initials: H
authors.lastname: Santos
authors.forename: Volker
authors.initials: V
authors.lastname: Müller
authors.forename: Beate
authors.initials: B
authors.lastname: Averhoff
mesh_terms: D000150:Acinetobacter / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D005636:Fructosephosphates / Q000378:metabolism; D008353:Mannitol / Q000378:metabolism; D008355:Mannitol Phosphates / Q000378:metabolism; D008969:Molecular Sequence Data; D009997:Osmotic Pressure / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D013401:Sugar Alcohol Dehydrogenases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D005636:Fructosephosphates; D008355:Mannitol Phosphates; C030070:mannitol-1-phosphate; D008353:Mannitol; C027618:fructose-6-phosphate; D013401:Sugar Alcohol Dehydrogenases; C021544:mannitol-1-phosphate dehydrogenase; D010744:Phosphoric Monoester Hydrolases