Adenosine triphosphate: glutamine synthetase adenylyltransferase of Escherichia coli: two active molecular forms

MoGLN2 Is Important for Vegetative Growth, Conidiogenesis, Maintenance of Cell Wall Integrity and Pathogenesis of Magnaporthe oryzae

Glutamine is a non-essential amino acid that acts as a principal source of nitrogen and nucleic acid biosynthesis in living organisms. In Saccharomyces cerevisiae, glutamine synthetase catalyzes the synthesis of glutamine. To determine the role of glutamine synthetase in the development and pathogenicity of plant fungal pathogens, we used S. cerevisiae Gln1 amino acid sequence to identify its orthologs in Magnaporthe oryzae and named them MoGln1, MoGln2, and MoGln3. Deletion of MoGLN1 and MoGLN3 showed that they are not involved in the development and pathogenesis of M. oryzae. Conversely, ΔMogln2 was reduced in vegetative growth, experienced attenuated growth on Minimal Medium (MM), and exhibited hyphal autolysis on oatmeal and straw decoction and corn media. Exogenous l-glutamine rescued the growth of ΔMogln2 on MM. The ΔMogln2 mutant failed to produce spores and was nonpathogenic on barley leaves, as it was unable to form an appressorium-like structure from its hyphal tips. Furthermore, deletion of MoGLN2 altered the fungal cell wall integrity, with the ΔMogln2 mutant being hypersensitive to H2O2. MoGln1, MoGln2, and MoGln3 are located in the cytoplasm. Taken together, our results shows that MoGLN2 is important for vegetative growth, conidiation, appressorium formation, maintenance of cell wall integrity, oxidative stress tolerance and pathogenesis of M. oryzae.

Fic and non-Fic AMPylases: protein AMPylation in metazoans

Protein AMPylation refers to the covalent attachment of an AMP moiety to the amino acid side chains of target proteins using ATP as nucleotide donor. This process is catalysed by dedicated AMP transferases, called AMPylases. Since this initial discovery, several research groups have identified AMPylation as a critical post-translational modification relevant to normal and pathological cell signalling in both bacteria and metazoans. Bacterial AMPylases are abundant enzymes that either regulate the function of endogenous bacterial proteins or are translocated into host cells to hijack host cell signalling processes. By contrast, only two classes of metazoan AMPylases have been identified so far: enzymes containing a conserved filamentation induced by cAMP (Fic) domain (Fic AMPylases), which primarily modify the ER-resident chaperone BiP, and SelO, a mitochondrial AMPylase involved in redox signalling. In this review, we compare and contrast bacterial and metazoan Fic and non-Fic AMPylases, and summarize recent technological and conceptual developments in the emerging field of AMPylation.

Novel polyadenylylation-dependent neutralization mechanism of the HEPN/MNT toxin/antitoxin system

The two-gene module HEPN/MNT is predicted to be the most abundant toxin/antitoxin (TA) system in prokaryotes. However, its physiological function and neutralization mechanism remains obscure. Here, we discovered that the MntA antitoxin (MNT-domain protein) acts as an adenylyltransferase and chemically modifies the HepT toxin (HEPN-domain protein) to block its toxicity as an RNase. Biochemical and structural studies revealed that MntA mediates the transfer of three AMPs to a tyrosine residue next to the RNase domain of HepT in Shewanella oneidensis. Furthermore, in vitro enzymatic assays showed that the three AMPs are transferred to HepT by MntA consecutively with ATP serving as the substrate, and this polyadenylylation is crucial for reducing HepT toxicity. Additionally, the GSX₁₀DXD motif, which is conserved among MntA proteins, is the key active motif for polyadenylylating and neutralizing HepT. Thus, HepT/MntA represents a new type of TA system, and the polyadenylylation-dependent TA neutralization mechanism is prevalent in bacteria and archaea.

Characterization and improved properties of Glutamine synthetase from Providencia vermicola by site-directed mutagenesis

In this study, a novel gene for Glutamine synthetase was cloned and characterized for its activities and stabilities from a marine bacterium Providencia vermicola (PveGS). A mutant S54A was generated by site directed mutagenesis, which showed significant increase in the activity and stabilities at a wide range of temperatures. The K_m values of PveGS against hydroxylamine, ADP-Na₂ and L-Glutamine were 15.7 ± 1.1, (25.2 ± 1.5) × 10^-5 and 32.6 ± 1.7 mM, and the k_cat were 17.0 ± 0.6, 9.14 ± 0.12 and 30.5 ± 1.0 s^-1 respectively. In-silico-analysis revealed that the replacement of Ser at 54th position with Ala increased the catalytic activity of PveGS. Therefore, catalytic efficiency of mutant S54A had increased by 3.1, 0.89 and 2.9-folds towards hydroxylamine, ADP-Na₂ and L-Glutamine respectively as compared to wild type. The structure prediction data indicated that the negatively charged pocket becomes enlarged and hydrogen bonding in Ser54 steadily promotes the product release. Interestingly, the residual activity of S54A mutant was increased by 10.7, 3.8 and 3.8 folds at 0, 10 and 50 °C as compared to WT. Structural analysis showed that S54A located on the loop near to the active site improved its flexibility due to the breaking of hydrogen bonds between product and enzyme. This also facilitated the enzyme to increase its cold adaptability as indicated by higher residual activity shown at 0 °C. Thus, replacement of Ala to Ser54 played a pivotal role to enhance the activities and stabilities at a wide range of temperatures.

Enzymes Involved in AMPylation and deAMPylation

Posttranslational modifications are covalent changes made to proteins that typically alter the function or location of the protein. AMPylation is an emerging posttranslational modification that involves the addition of adenosine monophosphate (AMP) to a protein. Like other, more well-studied posttranslational modifications, AMPylation is predicted to regulate the activity of the modified target proteins. However, the scope of this modification both in bacteria and in eukaryotes remains to be fully determined. In this review, we provide an up to date overview of the known AMPylating enzymes, the regulation of these enzymes, and the effect of this modification on target proteins.

Omega-aminoalkyl agaroses in the resolution of enzymes involved in regulation of glutamine metabolism

Systematic examination of a homologous series of omega-aminoalkyl agaroses showed that the pentyl derivative (Seph-C5-NH2) was best suited for the retention and subsequent separation of several proteins involved in the regulation of glutamine metabolism in Escherichia coli, including: glutamine synthetase [EC 6.3.1.2; L-glutamate:ammonia ligase (ADP-forming)], ATP:glutamine synthetase adenylyltransferase (EC 2.7.7.42), the PII regulatory protein which regulates the adenylylation and deadenylylation activities of the adenylyltransferase, the UTP:PII protein uridylyltransferase, and the uridylyl removing enzyme which catalyzes the removal of uridylyl groups from uridylylated PII protein. Resolution of these proteins was achieved by gradually increasing the concentration of KCl in the eluant, which resulted in consecutive detachment of the proteins from the column. Proteins that co-elute from a DEAE-cellulose column can be resolved and further purified on epsilon-aminopentyl agarose, probably due to the fact that with the homologous series it is possible to adjust the contribution of hydrophobic interactions for optimal resolution.

Modulation of glutamine synthetase adenylylation and deadenylylation is mediated by metabolic transformation of the P II -regulatory protein

Earlier studies showed that two protein components, P(I) and P(II), are concerned with the adenylylation and deadenylylation of Escherichia coli glutamine synthetase (EC 6.3.1.2). P(I) by itself catalyzes both adenylylation and deadenylylation, but its activity is modulated by the P(II)-protein and by glutamine, 2-oxoglutarate, ATP, and UTP, The P(II)-protein exists in two forms: one form, P(II)-AT, stimulates P(I)-catalyzed adenylylation activity in the absence of glutamine and makes this activity very sensitive to inhibition by 2-oxoglutarate; it does not affect deadenylylation activity. The other form, P(II)-DA, stimulates adenylylation only if glutamine is present, and also stimulates the deadenylylation activity of P(I), which is then dependent upon the presence of ATP and 2-oxoglutarate. Conversion of P(II)-AT to P(II)-DA requires the presence of UTP, ATP, and 2-oxoglutarate; it is catalyzed by an enzyme present in P(I) preparations. UTP may be directly involved in this conversion since P(II)-DA fractions reisolated by filtration through Sephadex G-100 contain small quantities of a bound uridine derivative that lacks the gamma-phosphoryl group of UTP. The activity of P(II)-DA, but not of P(II)-AT, is destroyed by treatment with snake-venom phosphodiesterase. ATP and 2-oxoglutarate apparently function as allosteric effectors for the conversion of P(II)-AT to P(I)-DA.