The plant Selaginella moellendorffii possesses enzymes for synthesis and hydrolysis of the compatible solutes mannosylglycerate and glucosylglycerate

Abstract

A mannosylglycerate synthase (MgS) gene detected in the genome of Selaginella moellendorffii was expressed in E. coli and the recombinant enzyme was purified and characterized. A remarkable and unprecedented feature of this enzyme was the ability to efficiently synthesize mannosylglycerate (MG) and glucosylglycerate (GG) alike, with maximal activity at 50 °C, pH 8.0 and with Mg(2+) as reaction enhancer. We have also identified a novel glycoside hydrolase gene in this plant's genome, which was functionally confirmed to be highly specific for the hydrolysis of MG and GG and named MG hydrolase (MgH), due to its homology with bacterial MgHs. The recombinant enzyme was maximally active at 40 °C and at pH 6.0-6.5. The activity was independent of cations, but Mn(2+) was a strong stimulator. Regardless of these efficient enzymatic resources we could not detect MG or GG in S. moellendorffii or in the extracts of five additional Selaginella species. Herein, we describe the properties of the first eukaryotic enzymes for the synthesis and hydrolysis of the compatible solutes, MG and GG.

Mycobacterium hassiacum recovers from nitrogen starvation with up-regulation of a novel glucosylglycerate hydrolase and depletion of the accumulated glucosylglycerate

“…Genes coding for proteins with significant amino acid identity to MgH could be detected in mycobacterial genomes but, unlike the GG biosynthetic genes identified in all the available genomes, mgH homologues were, with a few exceptions, almost exclusively detected in RGM (Table 1). The characterization of the M. hassiacum enzyme confirmed that, unlike the MgHs from the thermophilic bacteria Thermus thermophilus and Rubrobacter radiotolerans or the eukaryotic MgH from Selaginella moellendorffii that hydrolyze MG and GG alike, GG was by far the preferred substrate of the M. hassiacum enzyme, for which we propose the designation GG hydrolase (GgH)2425.…”

“…Recently, a glycosyl hydrolase able to hydrolyze mannosylglycerate (MG), a GG-related osmolyte common in hyperthermophilic archaea and some thermophilic bacteria, was identified in Thermus thermophilus and designated mannosylglycerate hydrolase (MgH)24. Despite the fact that this organism only accumulates MG and not GG, MgH was also shown to efficiently hydrolyze GG, as were the functional MgHs detected in Rubrobacter radiotolerans and in the primitive plant Selaginella moellendorffii 25.…”

Dealing with salinity extremes and nitrogen limitation – an unexpected strategy of the marine bacterium Dinoroseobacter shibae

“…Until now, no experimental evidence for the occurrence of GGA in α‐proteobacteria was found. It has been found in cyano‐ and γ‐proteobacteria and in the archaeon Methanohalophilus portucalensis , the aquificae Persephonella marina and, recently, in the plant Selaginella moellendorffii (Robertson et al ., ; Cánovas et al ., ; Goude et al ., ; Costa et al ., ; Empadinhas and da Costa, ; Nobre et al ., ).…”

Heterosides – compatible solutes occurring in prokaryotic and eukaryotic phototrophs

“…Recently, the genes coding for GGA and MGA synthesis enzymes were characterised in the primitive land plant Selaginella moellendorffii (Nobre et al . ). The authors’ provided evidence that the genes for these enzymes were probably acquired via horizontal gene transfer from MGA‐accumulating bacteria.…”

“…Related genes were also detected in many other genomes of red algae and other eukaryotes, including green algae and fungi, from which no MGA or GGA accumulation has ever been reported (Borges et al 2014). Recently, the genes coding for GGA and MGA synthesis enzymes were characterised in the primitive land plant Selaginella moellendorffii (Nobre et al 2013). The authors' provided evidence that the genes for these enzymes were probably acquired via horizontal gene transfer from MGA-accumulating bacteria.…”