SURVEY AND SUMMARY Gallia, Gary L; Johnson, Edward M; Khalili, Kamel
Nucleic acids research,
09/2000, Letnik:
28, Številka:
17
Journal Article
Recenzirano
Puralpha is a ubiquitous, sequence-specific DNA- and RNA-binding protein which is highly conserved in eukaryotic cells. Puralpha has been implicated in diverse cellular functions, including ...transcriptional activation and repression, translation and cell growth. Moreover, this protein has been shown to be involved in regulating several human viruses which replicate in the central nervous system (CNS), including human immunodeficiency virus type I (HIV-1) and JC virus (JCV). Puralpha exerts part of its activity by interacting with cellular proteins, including pRb, E2F, cyclin A, Sp1 and members of the Y-box family of proteins, including YB-1 and MSY1, as well as viral proteins such as polyomavirus large T-antigen and HIV-1 Tat. The ability of Puralpha to interact with its target DNA sequence and to associate with several viral and cellular proteins is modulated by RNA. Puralpha has also been shown to be involved in cell growth and proliferation. Its association with pRb, E2F and cyclin A coupled with its fluctuating levels throughout the cell cycle, position Puralpha as a crucial factor in the cell cycle. Moreover, microinjection studies demonstrate that Puralpha causes either a G<1< or G<2< arrest depending on the cell cycle time of injection. The gene encoding Puralpha has been localized to a human locus which is frequently deleted in myelogenous leukemias and other cancers and Puralpha gene deletions have been detected in many cases of lymphoid cancers. The following review details the structural characteristics of Puralpha, its family members and the involvement of this protein in regulating various cellular and viral genes, viral replication and cell growth.
The activation of the thiol of glutathione (GSH) bound in the active site of the class mu glutathione transferase M1-1 from rat involves a hydrogen-bonding network that includes a direct ...(first-sphere) interaction between the hydroxyl group of Y6 and the sulfur of GSH and second-sphere interactions involving a hydrogen bond between the main-chain amide N-H of L12 and the hydroxyl group of Y6 and an on-face hydrogen bond between the hydroxyl group of T13 and the π-electron cloud of Y6 (i.e., T13-OH- - -π-Y6-OH- - --SG). The functions of these hydrogen bonds have been examined with a combination of site-specific mutagenesis and X-ray crystallography. The hydroxyl group of Y6 has a normal pK a of about 10 even though it is shielded from solvent and is in a largely hydrophobic environment. The apparent pK a of GSH in the binary Y6F·GSH complex is increased by 1.6 log units, and the reactivity of the enzyme-bound nucleophile is reduced. The catalytic properties of the Y6L mutant are identical to those of Y6F, suggesting that the weakly polar on-edge interaction between the aromatic ring and sulfur has no influence on catalysis. The refined three-dimensional structure of the Y6F mutant in complex with GSH shows no major structural perturbation of the protein other than a change in the coordination environment of the sulfur. Removal of the second-sphere influence of the on-face hydrogen bond between the hydroxyl group of T13 as in the T13V and T13A mutants elevates the pK a of enzyme-bound GSH by about 0.7 pK a units. Crystal structures of these mutants show that structural changes in the active site are minor and suggest that the changes in pK a of E·GSH are due to the presence or absence of the on-face hydrogen bond. The T13S mutant has a completely different side-chain hydrogen-bonding geometry than T13 in the native enzyme and catalytic properties similar to the T13A and T13V mutants consistent with the absence of an on-face hydrogen bond. The γ-methyl group of T13 is essential in enforcing the on-face hydrogen bond geometry and preventing the hydroxyl group from forming more favorable conventional hydrogen bonds.
Background: Antigen receptor ligation induces apoptosis of B lymphocytes, but the molecular mechanisms underlying induction of apoptosis remain unclear, although the growing family of ...IL-1β–converting enzyme cysteine proteases (caspases) are recognized to be major effectors of cellular death. Objective: We sought to delineate and compare the rescue of B-cell apoptosis through CD40 ligand-CD40 interaction and cyclic adenosine monophosphate (cAMP)–dependent protein kinase A in human B cells. Methods: By using tonsillar B cells and the B-lymphoblastoid cell line Ramos, rescue from B-cell apoptosis was compared, as were signaling pathways after activation of cells through CD40 and the adenosine A2 receptor. Results: Both CD40 ligand-CD40 interaction and activation of intracellular cAMP rescue B cells from apoptosis after antigen receptor ligation. Although these pathways do not overlap, they converge by preventing the anti-IgM–induced activation of CPP32 (caspase 3), a member of the IL-1β–converting enzyme protease family. Conclusion: These data indicate that the cAMP-protein kinase A–dependent and CD40-signaling pathways regulate B-cell survival and converge at a common point, the inhibition of antigen receptor–induced activation of caspases. (J Allergy Clin Immunol 2000;105:522-31.)
This study was designed to examine the degree to which relationships of community power structures, school board behavior types and superintendent leadership styles exist in Oklahoma public schools. ...The study also explored the impact these relationships have on superintendent tenure and student achievement in Oklahoma. The study is based on the 1971 research of McCarty and Ramsey, with follow up studies by Hess (1994), Smith (1998) and Lere (2004). The study is a descriptive inferential study using the results of surveys mailed to all public school superintendents and school board presidents in Oklahoma. The questionnaire was originally designed by Hess in 1994 for use in Wisconsin and modified by Smith in 1998 for use in North Carolina. The survey sought to determine if the four theoretical categories of community power structures, school board types and superintendent leadership styles exist in Oklahoma school districts and the impact they have on student achievement. In addition, selected economic, social, political and demographic variables were examined along with district API scores for possible affects on the relationship types and student achievement. There was a good (53%) return from the superintendents, but a little weaker (24%) return rate by the school board presidents. The return rate of paired districts (92, 17%) allows some limited inferred predictions. From the paired responses the prediction can be made that relationship types and demographics have some impact on student achievement in Oklahoma. It can also be assumed that the combination of the two will likewise have an impact on student achievement. The data revealed evidence that all categories of community power structures, school board types and superintendent leadership styles existed in Oklahoma school districts. This follows and supports prior research indicating a substantial relationship exists between leadership and student achievement. It was also observed that demographics have an impact on the relationship between superintendents and school boards as well as an impact on student achievement. Also discussed are the implications for a need of staff development programs for superintendents and school board presidents and possible need for future studies.
Gq is the heterotrimeric guanine nucleotide-binding protein that activates the beta isoforms of phosphatidyl-inositol-specific phospholipase C (PI-PLC). The Gq alpha-subunit polypeptide (alpha qa) ...was N-terminally modified by addition of a 9-aa sequence, YPYDVPDYA. Placement of the 9-aa epitope tag at the N terminus allowed expression of functional alpha q polypeptides and selective identification of plasmid-expressed wild-type and mutant G-protein alpha subunits. Mutation of glutamine-209 to leucine in the N-terminally epitope-tagged alpha q (N(epi) alpha qQ209L) inhibited GTPase activity and persistently activated PI-PLC, resulting in high steady-state levels of inositol phosphates. The elevated levels of inositol phosphates resulting from N(epi) alpha qQ209L expression were similar to those obtained with carbachol activation of the M1 muscarinic acetylcholine receptor. The Gq-coupled M1 receptor, which stimulates PI-PLC activity, and phorbol esters, acting via protein kinase C, activate the cytoplasmic mitogen-activated protein kinase in COS cells. However, the constitutive activation of PI-PLC enzymatic activity resulting from expression of GTPase-deficient alpha q was unable to persistently activate this kinase. The results indicate that persistent PI-PLC activation is insufficient to sustain the stimulation of a cytoplasmic serine/threonine protein kinase regulated by Gq-coupled receptor signal-transduction pathways.
To determine the prevalence and significance of hepatitis C virus infection in kidney transplant recipients, paired serum samples collected from 100 renal allograft recipients on admission for kidney ...transplantation and 1 yr after transplantation were tested for antibody to hepatitis C virus with second-generation enzyme immunoassay and recombinant immunoblot assay and for hepatitis C virus RNA with reverse transcription-polymerase chain reaction. Before kidney transplantation, hepatitis C virus antibody was detected with second-generation enzyme immunoassay in 18 patients (12 second-generation recombinant immunoblot assay-positive, 6 second-generation recombinant immunoblot assay-indeterminate). Nine of 12 second-generation recombinant immunoblot assay-positive and 2 of 6 second-generation recombinant immunoblot assay-indeterminate samples were hepatitis C virus RNA positive. In addition, 7 of 82 patients who had no detectable antibody on second-generation enzyme immunoassay or second-generation recombinant immunoblot assay were hepatitis C virus RNA positive. After kidney transplantation, hepatitis C virus antibody was detected in 19 patients (12 second-generation recombinant immunoblot assay-positive, 7 second-generation recombinant immunoblot assay-indeterminate, 14 seropositive for hepatitis C virus antibody). Eleven of 12 patients with second-generation recombinant immunoblot assay-positive results and 4 of 7 with second-generation recombinant immunoblot assay-indeterminate results were positive for hepatitis C virus RNA. Hepatitis C virus RNA was present in 28 patients 1 yr after kidney transplantation. Six patients appeared to have acquired active hepatitis C virus infection 1 yr after kidney transplantation (seroconverted to hepatitis C virus RNA positivity).
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