The remarkable structural and functional organization of the eukaryotic pyruvate dehydrogenase complexes.

The three-dimensional reconstruction of the bovine kidney pyruvate dehydrogenase complex (M(r) approximately 7.8 x 10(6)) comprising about 22 molecules of pyruvate dehydrogenase (E(1)) and about 6 molecules of dihydrolipoamide dehydrogenase (E(3)) with its binding protein associated with the 60-subunit dihydrolipoamide acetyltransferase (E(2)) core provides considerable insight into the structural and functional organization of the largest multienzyme complex known. The structure shows that potentially 60 centers for acetyl-CoA synthesis are organized in sets of three at each of the 20 vertices of the pentagonal dodecahedral core. These centers consist of three E(1) molecules bound to one E(2) trimer adjacent to an E(3) molecule in each of 12 pentagonal openings. The E(1) components are anchored to the E(1)-binding domain of the E(2) subunits through an approximately 50-A-long linker. Three of these linkers emanate from the outside edges of the triangular base of the E(2) trimer and form a cage around its base that may shelter the lipoyl domains and the E(1) and E(2) active sites. The docking of the atomic structures of E(1) and the E(1) binding and lipoyl domains of E(2) in the electron microscopy map gives a good fit and indicates that the E(1) active site is approximately 95 A above the base of the trimer. We propose that the lipoyl domains and its tether (swinging arm) rotate about the E(1)-binding domain of E(2,) which is centrally located 45-50 A from the E(1), E(2), and E(3) active sites, and that the highly flexible breathing core augments the transfer of intermediates between active sites.

Direct evidence for the size and conformational variability of the pyruvate dehydrogenase complex revealed by three-dimensional electron microscopy. The "breathing" core and its functional relationship to protein dynamics.

Structural studies by three-dimensional electron microscopy of the Saccharomyces cerevisiae truncated dihydrolipoamide acetyltransferase (tE(2)) component of the pyruvate dehydrogenase complex reveal an extraordinary example of protein dynamics. The tE(2) forms a 60-subunit core with the morphology of a pentagonal dodecahedron and consists of 20 cone-shaped trimers interconnected by 30 bridges. Frozen-hydrated and stained molecules of tE(2) in the same field vary in size approximately 20%. Analyses of the data show that the size distribution is bell-shaped, and there is an approximately 40-A difference in the diameter of the smallest and largest structures that corresponds to approximately 14 A of variation in the length of the bridge between interconnected trimers. Companion studies of mature E(2) show that the complex of the intact subunit exhibits a similar size variation. The x-ray structure of Bacillus stearothermophilus tE(2) shows that there is an approximately 10-A gap between adjacent trimers and that the trimers are interconnected by the potentially flexible C-terminal ends of two adjacent subunits. We propose that this springlike feature is involved in a thermally driven expansion and contraction of the core and, since it appears to be a common feature in the phylogeny of pyruvate dehydrogenase complexes, protein dynamics is an integral component of the function of these multienzyme complexes.

One-step purification of the recombinant catalytic subunit of pyruvate dehydrogenase phosphatase.

A facile one-step affinity chromatographic purification of the recombinant catalytic subunit (PDPc) of bovine pyruvate dehydrogenase phosphatase (PDP) to near homogeneity is described. PDPc binds in the presence of Ca(2+) to the inner lipoyl domain (L2) of the dihydrolipoamide acetyltransferase component (E2) of the mammalian pyruvate dehydrogenase complex. The affinity column consists of a glutathione S-transferase (GST)-L2 fusion protein bound to glutathione-Sepharose 4B beads. An extract of transformed Escherichia coli cells containing 50 mM Tris buffer (pH 7.5), 2 mM CaCl(2), 5 mM MgCl(2,) 150 mM NaCl, 0.5 mM dithiothreitol, 1% Triton X-100, and l M urea was passed through the affinity column, and the column was washed extensively with this buffer mixture. PDPc was eluted with 50 mM Tris buffer (pH 7.5) containing 5 mM MgCl(2), 0.5 mM dithiothreitol, and 1 mM EGTA. Approximately 22 mg of highly purified PDPc was obtained from 10 g (wet weight) of transformed cells. The preparation contained a small amount of a "nicked" form of PDPc. The cleavage is between Arg-394 and Arg-395.

Medical records and privacy: empirical effects of legislation.

OBJECTIVE: To determine the effects of state legislation requiring patient informed consent prior to medical record abstraction by external researchers for a specific study. DATA SOURCES/STUDY SETTING: Informed consent responses obtained from November 1997 through April 1998 from members of a Minnesota-based IPA model health plan. STUDY DESIGN: Descriptive case study of consent to gain access to medical records for a pharmaco-epidemiologic study of seizures associated with use of a pain medication that was conducted as part of the FDA's post-marketing safety surveillance program to evaluate adverse events associated with approved drugs. DATA COLLECTION: The informed consent process approved by an institutional review board consisted of three phases: (1) a letter from the health plan's medical director requesting participation, (2) a second mailing to nonrespondents, and (3) a follow-up telephone call to nonrespondents. PRINCIPAL FINDINGS: Of 140 Minnesota health plan members asked to participate in the medical records study, 52 percent (73) responded and 19 percent (26) returned a signed consent form authorizing access to their records for the study. For 132 study subjects enrolled in five other health plans in states where study-specific consent was not required, health care providers granted access to patient medical records for 93 percent (123) of the members. CONCLUSION: Legislation requiring patient informed consent to gain access to medical records for a specific research study was associated with low participation and increased time to complete that observational study. Efforts to protect patient privacy may come into conflict with the ability to produce timely and valid research to safeguard and improve public health.

Role of technology assessment in health benefits coverage for medical devices.

With the profusion of new medical technology, managed care organizations are faced with the challenge of determining which medical devices and services warrant health benefits coverage. To aid in this decision-making process, managed care companies turn to technology assessment, a process that differs from the Food and Drug Administration's review of medical devices. Health plans typically use a structured approach to implementing coverage requirements in employer group benefits contracts and use technology assessment to evaluate the scientific evidence of effectiveness to support coverage decisions. Also important is the societal context for decisions regarding coverage for new technologies and the options being considered by policy makers for accountability in technology assessment by private insurers and health plans.

Molecular cloning of the cDNA coding sequence of IL-2 receptor-gamma (gammac) from human and murine forebrain: expression in the hippocampus in situ and by brain cells in vitro.

IL-2 has been implicated in various neurobiological processes of the mammalian CNS. To understand how IL-2 acts in the brain, our lab has sought to determine the molecular pharmacological characteristics of brain IL-2 receptors (IL-2R). The lymphocyte IL-2Rgamma, an essential subunit for IL-2 signaling, is also a common subunit (gammac) for multiple immune cytokine receptors (e.g., IL-4R, IL-7R, IL-9R, IL-15R). Having previously cloned the alpha and beta subunits of the IL-2R heterotrimer complex from normal murine forebrain, we examined the hypothesis that the brain IL-2Rgamma is derived from the same or a closely related gene coding sequence as that expressed by lymphocytes. In this study, we cloned and sequenced the full-length IL-2Rgamma coding region from saline-perfused mouse forebrain and from a human hippocampal library. The cDNA sequences of IL-2Rgamma from human and murine brain were 100% homologous to their lymphocyte sequences. Northern blot analysis showed that the mRNA transcripts in murine brain were the expected size, but the predominant transcript expressed in the brain was different than in the spleen. Compared to the spleen, very low levels of IL-2Rgamma were expressed in the forebrain. In the murine hippocampus, a region where a number of neurobiological actions of IL-2 have been reported, IL-2Rgamma mRNA was detected over the dentate gyrus and CA1-CA4 by in situ hybridization histochemistry. IL-2Rgamma was found to be constitutively expressed by murine HN33.dw hippocampal neuronal cells, murine NB41A3 neuroblastoma cells, astrocyte-enriched mixed glial cell cultures, and in SCID mouse forebrain. The human cortical neuronal cell lines, HCN-1A and HCN-2, did not express the IL-2Rgamma gene. These data suggest the possibility that, in addition to being essential in IL-2 signaling in brain, IL-2Rgamma could be a common subunit (gammac) for multiple cytokine receptors which may be operative in the mammalian CNS.

Isolation of IL-2 receptor-beta cDNA clones from AtT-20 pituitary cells: constitutive expression and role in signal transduction.

Interleukin-2 (IL-2) has been shown to stimulate ACTH secretion by anterior pituitary cells and has been implicated in pathophysiological processes of the pituitary and brain in several major neuropsychiatric disorders. The present study tested the hypothesis that IL-2 receptor-beta (IL-2R beta), a constitutively expressed and essential subunit for IL-2 signaling in lymphocytes, is expressed by AtT-20 pituitary cells and involved in transducing intracellular signals induced by IL-2. We isolated and sequenced three overlapping IL-2R beta cDNA clones from AtT-20 pituitary cells representing key regions of the gene protein coding sequence. These cDNA clones including conserved sequences shared by growth hormone and prolactin as well as intracytoplasmic Src and JAK family homology domains of nonreceptor protein tyrosine kinases essential for IL-2 signaling in lymphocytes. Their nucleotide sequences were 100% homologous with those expressed by lymphocytes (together they comprised 70% of the full length coding sequence). The IL-2R beta gene is constitutively expressed by AtT-20 pituitary cells, and its transcription was upregulated after CRF stimulation. Species-specific Il-2 induced intracellular signals in AtT-20 cells known to be mediated by Il-2R beta, including a transient increase in c-myc nuclear proto-oncogene transcription and the dose-dependent induction of DNA replication as measured by [3H]thymidine incorporation. The IL-2-induced DNA replication signal was not delivered by heat inactivated IL-2 and was partially blocked by a murine anti-IL-2R beta monoclonal antibody. These studies suggest that IL-2R beta may be a critical target involved in mediating the neuroimmunological actions of this prototypical cytokine in endocrine cells.

Modulation of behavioral and neurochemical measures of forebrain dopamine function in mice by species-specific interleukin-2.

Interleukin-2 (IL-2) has recently been implicated as a modulator of brain neuronal function and in the pathogenesis of several major neuropsychiatric disorders involving the dopamine system (e.g. schizophrenia and Parkinson's disease). Little is known, however, about the effects of IL-2 on dopamine-mediated behaviors. A series of behavioral experiments were performed in mice to examine the hypothesis that species-specific IL-2 could modify behaviors known to be mediated by forebrain dopamine pathways. IL-2 administered subcutaneously produced a robust increase in locomotor activity in an elevated plus-maze. No effects of the cytokine were evident on measures of acoustic startle, prepulse inhibition of the startle response (PPI), or fearfulness. In complementary in vitro neurochemical experiments, to most closely assess physiologically relevant effects of the cytokine on dopamine release from striatal neurons, species-specific IL-2 as well as high performance liquid chromatography (HPLC) were used to measure endogenous dopamine release from striatal slices. IL-2 dose-dependently modulated veratrine-evoked release of endogenous dopamine in a biphasic pattern, increasing release at lower concentrations and inhibiting release at a high concentration of the cytokine. In radioligand competition binding experiments, IL-2 was not active at striatal binding sites for [3H]spiroperidol (D2-like receptors), [3H]mazindol binding (dopamine uptake sites) and [3H]SCH23390 (D1-like receptors), indicating that the neuromodulatory actions of IL-2 are not the result of direct or allosteric effects on dopamine receptors. Knowledge of the mechanisms by which IL-2 influences brain dopamine function could provide new insight into the pathophysiology of forebrain dopamine neurons seen in disorders such as Parkinson's disease and schizophrenia.

Molecular cloning of NPY-Y1 receptor cDNA from rat splenic lymphocytes: evidence of low levels of mRNA expression and [125I]NPY binding sites.

The present study addressed the question of whether the effects of neuropeptide Y (NPY) on parameters of cellular immune activity are mediated by the direct action of this neuropeptide on lymphocyte NPY receptors. A partial cDNA corresponding to bp 3-585 of the NPY-Y1 receptor coding sequence was cloned from rat splenic lymphocytes and found to have 100% nucleotide sequence homology with that segment of the NPY-Y1 receptor in brain. Basal levels of NPY-Y1 mRNA expression and [125I]NPY binding sites of rat splenic lymphocytes were markedly lower than in frontal cortex. These data provide the first direct evidence that cells of the immune system possess NPY receptors, and suggest that further study will be necessary to determine their physiological significance.