A new bacterial hydrolase specific for the compatible solutes α-d-mannopyranosyl-(1 → 2)-d-glycerate and α-d-glucopyranosyl-(1 → 2)-d-glycerate

The accumulation patterns and biosynthesis of compatible solutes in hyper/thermophiles have been extensively studied. However, there is little information available on their hydrolysis, leading us to search for enzymes for this activity. From the analysis of the genomes of several microorganisms known to accumulate α-d-mannopyranosyl-(1 → 2)-d-glycerate (mannosylglycerate, MG) or α-d-glucopyranosyl-(1 → 2)-d-glycerate (glucosylglycerate, GG) we were able to identify a likely candidate gene for the hydrolysis of these molecules. The Thermus thermophilus HB27 homologue encoded a putative enzyme with motifs of the GH63 and GH37 families of glycoside hydrolases. We expressed the gene from this thermophilic bacterium and from Rubrobacter radiotolerans, and confirmed that the recombinant enzymes, here designated mannosylglycerate hydrolase (MgH), specifically hydrolysed MG (or GG) to mannose (or glucose) and glycerate. Both enzymes were highly stable and maximally active at temperatures close to each organisms’ optimal growth temperatures (half-lives of 15.4 ± 0.5 h at 55 °C and 16.1 ± 0.4 h at 70 °C) but at low pH (4.0–4.5). Cations were not required for their activity and each enzyme exhibited Michaelis–Menten kinetics at 50 °C and 70 °C, respectively, with comparable catalytic efficiencies towards MG and GG. Herein, we purified and characterized a novel and highly specific MG- and GG-hydrolyzing enzyme that represent an attractive tool for development of enzymatic assays for quantification of these solutes, which seem to be more prevalent in microorganisms than initially suspected.

► The first mannosylglycerate (MG) and glucosylglycerate (GG)-specific hydrolase.
► The new hydrolase is distributed throughout bacteria but absent from archaea.
► Efficient hydrolysis of both organic solutes occurs at low pH in vitro.
► A mechanism for the recycling of MG or GG has been identified.