Crystal structures of beryllium fluoride-free and beryllium fluoride-bound CheY in complex with the conserved C-terminal peptide of CheZ reveal dual binding modes specific to CheY conformation

Chemotaxis, the environment-specific swimming behavior of a bacterial cell is controlled by flagellar rotation. The steady-state level of the phosphorylated or activated form of the response regulator CheY dictates the direction of flagellar rotation. CheY phosphorylation is regulated by a fine equilibrium of three phosphotransfer activities: phosphorylation by the kinase CheA, its auto-dephosphorylation and dephosphorylation by its phosphatase CheZ. Efficient dephosphorylation of CheY by CheZ requires two spatially distinct protein-protein contacts: tethering of the two proteins to each other and formation of an active site for dephosphorylation. The former involves interaction of phosphorylated CheY with the small highly conserved C-terminal helix of CheZ (CheZ(C)), an indispensable structural component of the functional CheZ protein. To understand how the CheZ(C) helix, representing less than 10% of the full-length protein, ascertains molecular specificity of binding to CheY, we have determined crystal structures of CheY in complex with a synthetic peptide corresponding to 15 C-terminal residues of CheZ (CheZ(200-214)) at resolutions ranging from 2.0 A to 2.3A. These structures provide a detailed view of the CheZ(C) peptide interaction both in the presence and absence of the phosphoryl analog, BeF3-. Our studies reveal that two different modes of binding the CheZ(200-214) peptide are dictated by the conformational state of CheY in the complex. Our structures suggest that the CheZ(C) helix binds to a "meta-active" conformation of inactive CheY and it does so in an orientation that is distinct from the one in which it binds activated CheY. Our dual binding mode hypothesis provides implications for reverse information flow in CheY and extends previous observations on inherent resilience in CheY-like signaling domains.     

The inhibition of ATP-dependent shape change of human erythrocyte ghosts correlates with an inhibition of Mg(2+)-ATPase activity by fluoride and aluminofluoride complexes.

The vanadate-sensitive Mg(2+)-dependent ATPase activity of the human erythrocyte ghost is believed to be involved in the shape change events that convert echinocytic ghosts to smoothed forms (biconcave discs and stomatocytes). At physiological salt concentration, pH 7.4, 2 mM ATP, 5 mM Mg2+ and 1 mM EGTA, the Mg(2+)-ATPase activity of ghosts was inhibited strongly by millimolar concentrations of sodium fluoride: I50 = 1.31 +/- 0.23 mM (mean +/- S.D.; n = 12). The addition of aluminium chloride to 15 microM reduced the concentration of NaF required for 50% inhibition to 0.76 +/- 0.21 mM (n = 10). Aluminium alone had only a small inhibitory effect on the ATPase activity (13 +/- 9%; n = 10). Desferrioxamine, a strong chelator of tervalent aluminium ion, failed to reverse the inhibition by fluoride and reversed the inhibition in the presence of aluminium and fluoride back to those values obtained with fluoride alone. Of several metal salts tested only beryllium sulfate was able to replace aluminium as an effective inhibitor in the presence of fluoride. Inhibition of the Mg(2+)-ATPase activity by fluoride and the aluminofluoride complexes correlated with an inhibition of the rate of MgATP-dependent change in red cell ghost shape from echinocytes to smoothed forms. All gross morphological changes of the smoothing process were affected, including the production of discocytes, stomatocytes and endocyctic vesicles.     

Selective intracellular beryllium localization in rat tissue by mass-resolved ion microprobe imaging

Beryllium absorption sites in the kidney and liver of rats have been located and imaged at approximately 70 nm lateral resolution with a scanning ion microprobe utilizing secondary ion mass spectrometry. Embedded sections and lyophilized cryosections of these organs were prepared after in vivo administration of beryllium in soluble form. Beryllium distribution images were correlated with the histological microstructure revealed by CN- images. In the kidney, beryllium concentrates selectively within the nuclei of proximal tubule cells and occasionally within modified podocytes or mesangial cells in the glomerulus. In the liver, beryllium is seen to localize within severely altered lysosomal structures as well as within hepatocyte nuclei. These observations are relevant to understanding aspects of the toxic and carcinogenic properties of absorbed beryllium compounds.     

Cytochemical study of abnormal intranuclear structures rich in beryllium

During prolonged intoxication with beryllium sulphate, intranuclear beryllium-rich structures (IBRS) develop mainly in the cells of the convoluted tubules of the kidney. These structures are constituted by the accumulation of dense granules approximately 20 nm in diameter. The present work shows: 1) by electron probe microanalysis that IBRS are rich in phosphorus and calcium, and 2) by high resolution ion microanalysis that the granules are rich in beryllium and proteins. Staining with thallium alcoholate and regressive staining with ethylenediaminetetraacetate (EDTA) seem to demonstrate the presence of ribonucleoproteins in the granules. But the richness in calcium and phosphorus makes it difficult to interprete cytochemical reactions based on thallium and lead because complexes can be formed between calcium and thallium or lead, and between phosphorus and lead. Extraction with EDTA and digestion with RNase carried out on floating slices fixed with glutaraldehyde and embedded in glycol methacrylate show that: 1) the positive response of IBRS to cytochemical techniques used seems due solely to calcium; 2) the RNase forms a stable complex with a constituent of the granules that could be the highly phosphorylated acidic protein that binds preferentially to beryllium described by Parker and Stevens.     

Glycogen synthase kinase-3 inhibition by lithium and beryllium suggests the presence of two magnesium binding sites.

Lithium inhibits (Li(+)) glycogen synthase kinase-3 (GSK-3) by competition for magnesium (Mg(2+)), but not ATP or substrate. Here, we show that the group II metal ion beryllium (Be(2+)) is a potent inhibitor of GSK-3 and competes for both Mg(2+) and ATP. Be(2+) also inhibits the related protein kinase cdc2 at similar potency, but not MAP kinase 2. To compare the actions of Li(+) and Be(2+) on GSK-3, we have devised a novel dual inhibition analysis. When Be(2+) and ADP are present together each interferes with the action of the other, indicating that both agents inhibit GSK-3 at the ATP binding site. In contrast, Li(+) exerts no interference with ADP inhibition or vice versa. We find, however, that Li(+) and Be(2+) do interfere with each other. These results suggest that Be(2+) competes for two distinct Mg(2+) binding sites: one is Li(+)-sensitive and the other, which is Li(+)-insensitive, binds the Mg:ATP complex.