Mannitol-1-phosphate dehydrogenases/phosphatases: A family of novel bifunctional enzymes for bacterial adaptation to osmotic stress

Miriam Sand, Marta Rodrigues, José M. González, Valérie de Crécy-Lagard, Maria Helena Santos, Volker Müller, Beate Averhoff

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The nutritionally versatile soil bacterium Acinetobacter baylyiADP1 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 Mg2+ 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.

Original languageEnglish
Pages (from-to)711-719
Number of pages9
JournalEnvironmental Microbiology
Volume17
Issue number3
DOIs
Publication statusPublished - 1 Mar 2015

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