Morphine induces terminal micro-opioid receptor desensitization by sustained phosphorylation of serine-375

Morphine is a poor inducer of micro-opioid receptor (MOR) internalization, but a potent inducer of cellular tolerance. Here we show that, in contrast to full agonists such as [D-Ala(2)-MePhe(4)-Gly-ol]enkephalin (DAMGO), morphine stimulated a selective phosphorylation of the carboxy-terminal residue 375 (Ser(375)). Ser(375) phosphorylation was sufficient and required for morphine-induced desensitization of MOR. In the presence of full agonists, morphine revealed partial agonistic properties and potently inhibited MOR phosphorylation and internalization. Upon removal of the drug, DAMGO-desensitized receptors were rapidly dephosphorylated. In contrast, morphine-desensitized receptors remained at the plasma membrane in a Ser(375)-phosphorylated state for prolonged periods. Thus, morphine promotes terminal MOR desensitization by inducing a persistent modification of Ser(375).     

Establishing a versatile fermentation and purification procedure for human proteins expressed in the yeasts Saccharomyces cerevisiae and Pichia pastoris for structural genomics

We describe the introduction of the yeasts Saccharomyces cerevisiae and Pichia pastoris as eukaryotic hosts for the routine production of recombinant proteins for a structural genomics initiative. We have previously shown that human cDNAs can be efficiently expressed in both hosts using high throughput procedures. Expression clones derived from these screening procedures were grown in bioreactors and the over-expressed human proteins were purified, resulting in obtaining significant amounts suitable for structural analysis. We have also developed and optimized protocols enabling a high throughput, low cost fermentation and purification strategy for recombinant proteins for both S. cerevisiae and P. pastoris on a scale of 5 to 10 mg. Both batch and fed batch fermentation methods were applied to S. cerevisiae. The fed batch fermentations yielded a higher biomass production in all the strains as well as a higher productivity for some of the proteins. We carried out only fed batch fermentations on P. pastoris strains. Biomass was produced by cultivation on glycerol, followed by feeding methanol as carbon source to induce protein expression. The recombinant proteins were expressed as fusion proteins that include a N-terminal His-tag and a C-terminal Strep-tag. They were then purified by a two-step chromatographic procedure using metal-affinity chromatography and StrepTactin-affinity chromatography. This was followed by gel filtration for further purification and for buffer exchange. This three-step purification procedure is necessary to obtain highly purified proteins from yeast. The purified proteins have successfully been subjected to crystallization and biophysical analysis.     

Structural features and mechanisms for sensing high osmolarity in microorganisms

During their lifetime, most organisms experience osmotic stress, mostly due to fluctuating external osmolarities, but also as a result of desiccation or freezing. Under these conditions, the ratio of osmolytes to water and macromolecules in the cells is significantly altered. To survive, cells must continuously sense these alterations and adapt accordingly. Osmolarity is a physico-chemical parameter that causes pleiotropic alterations in cell physiology. Recent research has revealed various mechanisms to sense high external osmolarity, based on monitoring cellular changes that are associated with the altered environment.     

Peanut Stripe Potyvirus Resistance in Peanut (Arachis Hypogaea L.) Plants Carrying Viral Coat Protein Gene Sequences

Peanut (Arachis hypogaea L.) lines exhibiting high levels of resistance to peanut stripe virus (PStV) were obtained following microprojectile bombardment of embryogenic callus derived from mature seeds. Fertile plants of the commercial cultivars Gajah and NC7 were regenerated following co-bombardment with the hygromycin resistance gene and one of two forms of the PStV coat protein (CP) gene, an untranslatable, full length sequence (CP2) or a translatable gene encoding a CP with an N-terminal truncation (CP4). High level resistance to PStV was observed for both transgenes when plants were challenged with the homologous virus isolate. The mechanism of resistance appears to be RNA-mediated, since plants carrying either the untranslatable CP2 or CP4 had no detectable protein expression, but were resistant or immune (no virus replication). Furthermore, highly resistant, but not susceptible CP2 T0 plants contained transgene-specific small RNAs. These plants now provide important germplasm for peanut breeding, particularly in countries where PStV is endemic and poses a major constraint to peanut production.     

Hypoxia-induced inhibition of whole cell membrane currents and ion transport of A549 cells

In excitable cells, hypoxia inhibits K channels, causes membrane depolarization, and initiates complex adaptive mechanisms. It is unclear whether K channels of alveolar epithelial cells reveal a similar response to hypoxia. A549 cells were exposed to hypoxia during whole cell patch-clamp measurements. Hypoxia reversibly inhibited a voltage-dependent outward current, consistent with a K current, because tetraethylamonium (TEA; 10 mM) abolished this effect; however, iberiotoxin (0.1 microM) does not. In normoxia, TEA and iberiotoxin inhibited whole cell current (-35%), whereas the K-channel inhibitors glibenclamide (1 microM), barium (1 mM), chromanol B293 (10 microM), and 4-aminopyridine (1 mM) were ineffective. (86)Rb uptake was measured to see whether K-channel modulation also affected transport activity. TEA, iberiotoxin, and 4-h hypoxia (1.5% O(2)) inhibited total (86)Rb uptake by 40, 20, and 35%, respectively. Increased extracellular K also inhibited (86)Rb uptake in a dose-dependent way. The K-channel opener 1-ethyl-2-benzimidazolinone (1 mM) increased (86)Rb uptake by 120% in normoxic and hypoxic cells by activation of Na-K pumps (+60%) and Na-K-2Cl cotransport (+170%). However, hypoxic transport inhibition was also seen in the presence of 1-ethyl-2-benzimidazolinone, TEA, and iberiotoxin. These results indicate that hypoxia, membrane depolarization, and K-channel inhibition decrease whole cell membrane currents and transport activity. It appears, therefore, that a hypoxia-induced change in membrane conductance and membrane potential might be a link between hypoxia and alveolar ion transport inhibition.     

Constructive effects of fluctuations in genetic and biochemical regulatory systems

Biochemical and genetic regulatory systems that involve low concentrations of molecules are inherently noisy. This intrinsic stochasticity has received considerable interest recently, leading to new insights about the sources and consequences of noise in complex systems of genetic regulation. However, most prior work was devoted to the reduction of fluctuation and the robustness of cellular function with respect to intrinsic noise. Here, we focus on several scenarios in which the inherent molecular fluctuations are not merely a nuisance, but act constructively and bring about qualitative changes in the dynamics of the system. It will be demonstrated that in many typical situations biochemical and genetic regulatory systems may utilize intrinsic noise to their advantage.     

Ontogeny has a phylogeny: background to adjunctive behaviors in pigeons and budgerigars

Animals coping with operant conditioning tasks often show behaviors that are not recorded by keys, levers and similar response transducers. Nevertheless, these adjunctive behaviors should not be disposed of by classifying them as incidental. Often they are found to be at least partially influenced by the experimentally programmed contingencies, and under certain conditions they can in turn influence conditioned behaviors. Here we describe the occurrence and characteristics of two such behaviors, stimulus grasping in operantly key-pecking pigeons and intra-delay stereotypies in a delayed matching-to-sample task with budgerigars. It is argued that for a proper account of these behaviors it is necessary to refer to a behavioral systems approach that appeals to longer ranging ontogenetic and phylogenetic histories than is usually considered in the psychological literature. The gaping towards on-key stimuli by pigeons is attributed to the hypothesis that operantly conditioned key-pecks probably relate to a grasp-pecking response that is normally executed towards non-edible items covering food. The intra-delay behaviors shown by the budgerigars are assumed to have originated from stress-induced displacement responses that adventitiously came under the influence of differential reinforcement contingencies. Finally, we discuss what kinds of evidence are needed to put these hypothetical explanations on a more certain footing.     

Dichotomy of autoreactive Th1 and Th2 cell responses to desmoglein 3 in patients with pemphigus vulgaris (PV) and healthy carriers of PV-associated HLA class II alleles

Pemphigus vulgaris (PV) is the most severe autoimmune bullous skin disorder and is primarily associated with circulating autoantibodies (autoAb) against desmoglein 3 (Dsg3). In light of recent evidence that autoreactive T cells are critical for the induction and regulation of Ab production, the goal of this study was to characterize and quantitate autoreactive T cells in patients with PV and healthy controls. Peripheral Dsg3-reactive Th cells from 28 patients with acute-onset, chronic active, and remittent PV were quantitated by MACS secretion assay. Dsg3-reactive Th2 cells were detected at similar frequencies in all studied PV patients, while the number of autoreactive Th1 cells exceeded those of Th2 cells in chronic active PV. In contrast, healthy carriers of the PV-associated HLA class II alleles, DRB1*0402 and DQB1*0503, exhibited exclusively Dsg3-reactive Th1 cell responses, while healthy carriers of other HLA class II alleles did not. Moreover, the presence of IgG1 and IgG4 against Dsg3 was directly related to the ratio of Dsg3-reactive Th1/Th2 cells. T cell recognition of Dsg3 was restricted by HLA-DRB1*0402 and DQB1*0503 in PV patients and Dsg3-responsive healthy donors. These observations strongly suggest 1) that the appearance of Dsg3-reactive Th2 cells is restricted to patients with PV; 2) that specific HLA class II alleles that are prevalent in PV are critical for T cell recognition of Dsg3 in PV patients and Dsg3-responsive healthy donors; and 3) that autoAb production is associated with both Th1 and Th2 cells.