The role of uridylyltransferase and PII in the regulation of the synthesis of glutamine synthetase in Escherichia coli

Advances in the enzymology of glutamine synthesis

Meister's proposal of a gamma-glutamyl-P intermediate in the glutamine synthetase reaction set the scene for understanding how the stepwise activation of the carboxyl group greatly increased its susceptibility toward nucleophilic attack and amide bond synthesis. Topics covered in this review include: the discovery of the enzymatic synthesis of glutamine; the role of glutamine synthetase in defining the thermodynamics of ATPases; early isotopic tracer studies of the synthetase reaction; the proposed intermediacy of gamma-glutamyl-phosphate; the mechanism of methionine sulfoximine inhibition; stereochemical mapping of the enzyme's active site; detection of enzyme reaction cycle intermediates; borohydride trapping of gamma-glutamyl-P; positional isotope exchanges catalyzed by glutamine synthetase; regulation of bacterial enzyme; and a brief account of how knowledge of the atomic structure of bacterial glutamine synthetase has clarified ligand binding interactions. Concluding remarks also address how the so-called "Protein Ligase Problem" may be solved by extending the catalytic versatility of carboxyl-group activating enzymes.

Nitrogen control in bacteria

Nitrogen metabolism in prokaryotes involves the coordinated expression of a large number of enzymes concerned with both utilization of extracellular nitrogen sources and intracellular biosynthesis of nitrogen-containing compounds. The control of this expression is determined by the availability of fixed nitrogen to the cell and is effected by complex regulatory networks involving regulation at both the transcriptional and posttranslational levels. While the most detailed studies to date have been carried out with enteric bacteria, there is a considerable body of evidence to show that the nitrogen regulation (ntr) systems described in the enterics extend to many other genera. Furthermore, as the range of bacteria in which the phenomenon of nitrogen control is examined is being extended, new regulatory mechanisms are also being discovered. In this review, we have attempted to summarize recent research in prokaryotic nitrogen control; to show the ubiquity of the ntr system, at least in gram-negative organisms; and to identify those areas and groups of organisms about which there is much still to learn.

Preliminary X-ray diffraction analysis of crystals of the PII protein from Escherichia coli

PII protein, which carries metabolic signals regulating the transcription and activity of glutamine synthetase in nitrogen assimilation in Escherichia coli, has been crystallized in space group P2(1) with a = 47.8 A, b = 62.9 A, c = 52.8 A and beta = 100.3 degrees and space group P2(1)2(1)2(1) with a = 52.2 A. b = 64.9 A and c = 100.1 A. Both the monoclinic crystals, which diffract beyond 3.0 A, and the orthorhombic crystals, which diffract beyond 2.5 A, probably have three molecules of 12,400 Da each in the crystallographic asymmetric unit.

CheA protein, a central regulator of bacterial chemotaxis, belongs to a family of proteins that control gene expression in response to changing environmental conditions

During bacterial chemotaxis, the binding of stimulatory ligands to chemoreceptors at the cell periphery leads to a response at the flagellar motor. Three proteins appear to be required for receptor-mediated control of swimming behavior, the products of the cheA, cheW, and cheY genes. Here we present the complete nucleotide sequence of the Salmonella typhimurium cheA gene together with the purification and characterization of its protein product. The protein is a 73,000 Mr cytoplasmic constituent. Amino acid-sequence comparisons indicate that it belongs to a family of bacterial regulatory proteins including the products of the cpxA, dctB, envZ, ntrB, phoR, phoM, and virA genes. Each member of this family has a conserved domain of approximately equal to 200 residues within its C terminus. We have previously shown that another chemotaxis protein, CheY, represents a domain of protein structure that has been conserved within a second large family of bacterial regulatory proteins. Each protein of the CheA family seems to function as a regulator of a different CheY homologue. Although each pair of proteins appears to produce a specialized response to a distinct type of stimulus, the relationships in primary structure suggest that a similar molecular mechanism may be involved.