Abstract
The genome of the halophilic archaea Haloferax mediterranei contains three ORFs that show homology with glutamine synthetase (GS) (glnA-1, glnA-2, and glnA-3). Previous studies have focused on the role of GlnA-1, suggesting that proteins GlnA-2 and GlnA-3 could play a different role to that of GS. Glutamine synthetase (EC 6.3.1.2) belongs to the class of ligases, including 20 subclasses of other different enzymes, such as aspartate–ammonia ligase (EC 6.3.1.1), glutamate–ethylamine ligase (EC 6.3.1.6), and glutamate–putrescine ligase (EC 6.3.1.11). The reaction catalyzed by glutamate–putrescine ligase is comparable to the reaction catalyzed by glutamine synthetase (GS). Both enzymes can bind a glutamate molecule to an amino group: ammonium (GS) or putrescine (glutamate–putrescine ligase). In addition, they present the characteristic catalytic domain of GS, showing significant similarities in their structure. Although these proteins are annotated as GS, the bioinformatics and experimental results obtained in this work indicate that the GlnA-2 protein (HFX_1688) is a glutamate–putrescine ligase, involved in polyamine catabolism. The most significant results are those related to glutamate–putrescine ligase’s activity and the analysis of the transcriptional and translational expression of the glnA-2 gene in the presence of different nitrogen sources. This work confirms a new metabolic pathway in the Archaea domain which extends the knowledge regarding the utilization of alternative nitrogen sources in this domain.
Highlights
Glutamine synthetase (GS; EC 6.3.1.2), which belongs to the class of ligases, can form carbon–nitrogen bonds using ATP
In the first node are all the GlnAs from species belonging to the Archaea domain, with the exception of two bacterial species (S. coelicolor and Streptomyces luteus)
Most of the proteins found in the other secondary node are species from the Halobacteriaceae family and other representatives of the Haloferacaceae, Natrialbaceae, and Halorubraceae families
Summary
Glutamine synthetase (GS; EC 6.3.1.2), which belongs to the class of ligases, can form carbon–nitrogen bonds using ATP This class includes 20 different subclasses of enzymes, including GS, aspartate–ammonia ligase (EC 6.3.1.1), glutamate–ethylamine ligase (EC 6.3.1.6), and glutamate–putrescine ligase (EC 6.3.1.11). GS acts with the glutamate synthase enzyme (GOGAT; EC 1.4.7.1), catalyzing the reductive transfer of the amide group from L-glutamine to 2-oxoglutarate. This reaction, which is dependent on reducing power, generates two molecules of L-glutamate, one of which is recycled as a substrate for the GS reaction, while the other is exported or used to produce other amino acids [5].
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